HEM pilot case · four regulatory architectures · one drought · Virmasvesi · Saimaa · Kemijoki
Virmasvesi/Iisvesi, a mid-sized boreal lake in Pohjois-Savo, has maintained water levels near the historical minimum winter level (MNW, ~97.45 m NN) through spring 2026 — a period when levels should have recovered following winter. The proximate cause is a low-snow winter (2025–2026) producing minimal snowmelt recharge. The structural cause is that bottom weir adjustment decisions, which would have partially restored levels, were not made. The regulatory framework governing weir operations is based on historical date-driven schedules and statistical thresholds, not on observed or anticipated hydrological endurance conditions. This case is the founding pilot for the Hydrological Endurance Monitor (HEM). It demonstrates the three-gap structure (measurement gap, sanction gap, correction gap) in a water resource management context, and illustrates how an endurance-based early warning index — HEPP — would have detected the emerging deficit weeks before conventional thresholds registered the condition as anomalous.
Virmasvesi (officially Iisvesi–Virmasvesi–Rasvanki, vesistötunnus 14.722.1.001) is a regulated boreal lake in the Pohjois-Savo region of central Finland. In autumn 2025, the water level fell to near minimum winter level. The following winter was characterised by significantly below-normal snow accumulation across the catchment. By May 2026, the lake had not recovered to seasonal norms despite inflow increasing as temperatures rose. The water level on 11 May 2026 was approximately 97.50 m NN, effectively at or near MNW (97.45 m).
This is anomalous. In a typical year, snowmelt between March and May produces a significant recharge pulse that raises water levels 0.3–0.8 m above the winter minimum. In spring 2026 this pulse was negligible: snow water equivalent had already approached zero before the melt season began in earnest, leaving only direct precipitation as the recharge source. Total inflow in May is estimated at 15–18 m³/s, rising toward 20–40 m³/s by late May, but insufficient to overcome the accumulated deficit.
Bottom weirs (pohjapadot) in the outlet system could have been adjusted in autumn 2025 or winter 2026 to reduce outflow and conserve water volume. This adjustment was not made. The decision-making framework governing weir operations is calendar-based and statistical: adjustments follow historical schedules tied to seasonal dates and long-run average flow conditions. The framework does not include a mechanism for detecting or responding to an emerging endurance deficit before conventional minimum thresholds are reached.
§ 02A prolonged period at or near MNW in a boreal lake produces cascading effects that accumulate over months rather than days. The most significant in the Virmasvesi context include:
| Effect | Mechanism | Timescale |
|---|---|---|
| Groundwater level decline | Lake acts as recharge source for surrounding aquifers; sustained low level reduces lateral recharge gradient | Weeks–months |
| Eutrophication acceleration | Shallow nearshore zones exposed or reduced; nutrient concentration in reduced water volume; sediment resuspension | Weeks–season |
| Shoreline and dock access | Private docks, boat launches, and riparian infrastructure become inaccessible below normal operating level | Immediate |
| Fish habitat degradation | Reduced littoral zone; thermal stratification compressed; spawning habitat affected in shallow bays | Weeks–season |
| Tourism and recreational use | Navigability reduced in shallow channels; beach access impaired | Immediate–season |
| Water intake reliability | Municipal and agricultural intakes approaching minimum operational depth | Weeks–months |
These effects are not catastrophic individually. Collectively they constitute a persistent reduction in the lake system's functional capacity — precisely the endurance concept that HEM is designed to quantify.
§ 03The Virmasvesi case illustrates the three-gap model (CN-007) operating in a water resource management context.
Water level at Iisvesi is monitored continuously (SYKE automatic station, WSFS-O). The data exists. What does not exist is a composite endurance index that integrates the water level trajectory, the snow water equivalent anomaly, the seasonal inflow forecast, and the regulatory response calendar into a single signal. Each variable is monitored in isolation. The combination that produces the anomaly — low starting level + low snow + calendar-bound regulation — is not synthesised into a warning. The measurement gap is not a data gap; it is an integration gap.
The regulatory framework does not impose costs on failing to adjust weirs in response to an emerging deficit. The framework is designed around avoiding floods and maintaining minimum flows for ecological and navigation purposes. It is not designed to detect or penalise the accumulation of endurance deficit before minimum thresholds are reached. A weir operator who declines to make a precautionary adjustment in October 2025 faces no consequence in November when the deficit is still below the regulatory threshold. By May 2026, when the consequence is visible, the window for low-cost intervention has long since closed.
The correction that would have been most effective — weir adjustment in autumn 2025 when the deficit was 10–20 cm and the winter snow forecast was already below average — required an anticipatory decision. No mechanism existed within the regulatory framework to prompt, request, or require such a decision. By spring 2026, the remaining correction options are limited: weir adjustment can slow further decline but cannot substitute for the recharge that did not arrive.
Mittausvaje: Tieto on olemassa hajallaan — vedenkorkeus, lumen vesiarvo, tulovirtamaennuste, säädöskalenteri. Niitä ei yhdistetä endurance-indikaattoriksi ennen kuin kynnysarvot ylittyvät.
Sanktiovaje: Ennakollisesta toimimattomuudesta ei seuraa kustannuksia. Pohjapadon säätämättä jättäminen syksyllä 2025 ei tuota vastuuta keväällä 2026.
Korjausvaje: Tehokkain korjaushetki — syksy 2025 — vaati ennakoivan päätöksen. Mekanismia sellaisen päätöksen pyytämiseen tai vaatimiseen ei ollut.
The Hydrological Endurance Pressure Proxy (HEPP) is a composite index integrating three components with configurable weights: Storage Deficit (SD, weight 0.40), Hydrological Stress Persistence (HSP, weight 0.35), and Recharge Failure (RF, weight 0.25). In the Virmasvesi context, these components would have behaved as follows.
| Component | Autumn 2025 | Winter 2025–26 | Spring 2026 |
|---|---|---|---|
| SD — Storage Deficit | Rising: level already below seasonal norm | Elevated: no snowmelt recovery | High: MNW contact in May anomalous |
| HSP — Stress Persistence | Low initially, rising as deficit extends | High: consecutive weeks below 90% rolling mean | Very high: persistent since autumn 2025 |
| RF — Recharge Failure | Moderate: autumn precipitation near average | High: snow water equivalent → 0 | High: no snowmelt pulse |
| HEPP composite | ~0.35–0.45 · Elevated | ~0.55–0.65 · Elevated–High | ~0.65–0.75 · High stress |
A HEPP threshold crossing of 0.50 in late autumn 2025 — approximately 5–6 months before the May 2026 observation — would have identified the emerging endurance deficit at a point when weir adjustment was both technically feasible and low-cost. This is the lead time advantage that CN-010 describes as the missing price signal: the endurance deficit accumulates and is detectable before conventional minimum thresholds are reached, but there is no instrument to translate the detection into a prompt for action.
§ 05The Virmasvesi case is not an operational failure. The regulatory framework functioned as designed. Weir operators followed applicable rules. SYKE monitoring systems produced accurate data. The failure is architectural: the regulatory design does not include an anticipatory layer.
SP-007 establishes that institutions inherit biological constraints from their human members, including status-based resistance to precautionary action that lacks an immediate trigger. An operator who adjusts a weir in October based on a projected deficit bears the full cost of the decision (including regulatory scrutiny if the projection proves conservative) while the benefit — avoided deficit months later — is diffuse and attributable to many factors. This cost-benefit structure predicts exactly the observed outcome: precautionary weir adjustment does not occur.
The HEPP instrument is designed to change this structure by providing an externally observable, time-stamped index that documents when the endurance condition crossed from Normal to Elevated to High. This does not compel action, but it makes inaction visible. A regulator or water authority reviewing the record in May 2026 can observe that HEPP crossed 0.50 in October 2025 — and that no weir adjustment was made before that date.
§ 06Research into the governing framework reveals a finding that fundamentally sharpens the institutional analysis. Virmasvesi/Iisvesi is part of the Rautalammin reitti — and the Rautalammin reitti is entirely unregulated. It is Finland's largest free-flowing inland waterway, running unregulated from Pielavesi to Konnevesi. The Kymijoki main channel downstream has 12 hydropower plants with ~220 MW combined capacity, but these are separated from the Rautalammin reitti by Konnevesi and operate on a different regulatory basis entirely.
This means the three-gap analysis must be revised upward in severity:
| Gap | Regulated lake | Rautalammin reitti (unregulated) |
|---|---|---|
| Measurement gap | Monitoring exists; integration gap only | Same integration gap, but no regulatory trigger at all |
| Sanction gap | Operator faces regulatory scrutiny for non-compliance | No operator; no licence; no obligation; no scrutiny |
| Correction gap | Permit modification path exists (AVI, vesilaki VL 18:3a) | No existing permit to modify; intervention requires new legal process |
The absence of regulation is not a neutral condition. For regulated lakes, the Water Act (vesilaki 587/2011, §18:3a) provides a mechanism: a padotus- ja juoksutusselvitys (impoundment and flow review) can be ordered to address drought conditions, and ELY-keskus can act as the state permit holder to adjust operations. For unregulated lakes, this mechanism does not exist. There is no permit to review, no holder to instruct, and no scheduled decision point at which endurance conditions enter institutional consideration.
The climate relevance is direct. Vesi.fi documents that the "kevätkuoppa" requirement in many regulation permits — the mandatory spring drawdown to create flood buffer — is becoming problematic as snow accumulation decreases and melt timing shifts earlier. For regulated lakes, this creates a known adaptation pathway: permits can be modified. For the Rautalammin reitti, the equivalent problem (low snow → no recharge → persistent deficit) has no equivalent institutional pathway.
For unregulated basins like Virmasvesi, HEM's institutional function shifts from prompt (flagging that a scheduled decision should be made differently) to document (creating a record that an endurance deficit is accumulating in a basin where no institutional actor is currently responsible for responding to it). This is a harder problem — the missing instrument is not just a better signal but a missing institutional role.
Three design implications follow. First, HEPP weights for snow-dependent unregulated basins should amplify the RF (Recharge Failure) component, reflecting the disproportionate role of snowmelt when no active flow management exists. Second, HEM should identify the responsible ELY-keskus district (Pohjois-Savon ELY in this case) and the relevant Water Act provision (VL 18:3a or VL 18:4 for emergency intervention) as part of the basin configuration. Third, the lead-time documentation function is especially important for unregulated basins: a HEPP series that crosses 0.50 in October creates a public record that the condition was detectable — and that no institutional mechanism existed to respond to it.
The Virmasvesi/Iisvesi 2025–2026 case demonstrates that hydrological endurance failure is detectable months before conventional thresholds register the anomaly. The failure is not a data failure or an operator failure. It is an institutional design failure: the regulatory framework lacks a mechanism for translating early endurance signals into anticipatory decisions. HEM HEPP is designed as that mechanism — not to predict water levels, but to make accumulating endurance deficits visible at the point when low-cost intervention remains possible.
Saimaa presents a fundamentally different institutional architecture from Virmasvesi — and the spring 2026 drought reveals its specific constraints as clearly as the Rautalammin case reveals its own.
Saimaa is formally unregulated: water levels follow natural variation. However, the 1991 bilateral treaty between Finland and Russia (the Saimaa–Vuoksi flow regulation agreement) permits deviation from natural discharge when water levels threaten to exceed ±50 cm from the long-term seasonal average — the normaalivyöhyke. The treaty also sets a minimum outflow floor and assigns decision authority in layers: Kaakkois-Suomen elinvoimakeskus (ELY) acts within the normal zone; the Ministry of Agriculture and Forestry (MMM) decides when economic damage or hydrological extremes require larger interventions.
In spring 2026 the mechanism activated at its outer limits. Discharge reductions began 23 March 2026. By 4 May 2026 the weekly average was reduced to 300 m³/s — the lowest in the treaty's history since 1991, and last seen in 2006. Despite this, Saimaa's level is projected to remain approximately 50 cm below the seasonal average through summer 2026 — potentially the lowest in nearly 50 years. ELY explicitly stated that no further reductions are available within the treaty framework.
The Saimaa case reveals a different failure mode than Virmasvesi. The institutional mechanism exists and activated correctly — but it has hard limits. The 1991 treaty sets a minimum outflow floor below which Finland cannot go regardless of lake level, because Vuoksi flows through Russian territory and the downstream consequences are governed by the bilateral agreement. When a two-year cumulative deficit combines with a low-snow winter and early spring, the treaty-constrained instrument reaches its boundary before the hydrological deficit does. The correction gap here is not an absent mechanism but an undersized one.
For HEPP, Saimaa is a case where the instrument's function is to document the pace at which the deficit accumulated relative to the speed at which the treaty mechanism could respond. The mechanism requires threshold exceedance before it activates; a two-year cumulative deficit that approaches the threshold slowly may not trigger early activation even when the endurance trajectory is clearly visible months in advance. The HEPP record from summer 2024 onward would have shown the persistent elevated regime — and the gap between instrument signal and institutional trigger.
§ 08Finland's northern rivers — Kemijoki, Oulujoki, Iijoki — represent the opposite end of the institutional spectrum from Virmasvesi. They are fully regulated systems where virtually every major lake and reservoir is managed for hydropower production. Kemijoki Oy operates eight power plants on the Kemijoki main channel alone; the river has been under continuous active management since the first plant opened in 1948. The combined regulated capacity of the Kemijoki system gives operators the ability to raise or lower reservoir levels by metres within a single season.
In hydrological terms this is maximum institutional control. In endurance terms it is a different kind of problem: the objective function of the regulation system is electricity production, not lake-level stability or ecological resilience. The water is there; the decision of how to use it is made by power company operators subject to their licence conditions and market incentives. When drought reduces inflow, regulated northern reservoirs face the same underlying hydrology as unregulated southern lakes — but the response mechanism is optimised for a different outcome.
| Attribute | Virmasvesi (unregulated) | Saimaa (treaty-constrained) | Kemijoki (power-regulated) |
|---|---|---|---|
| Regulation type | None — kansallisvesi | Natural + bilateral treaty | Full hydropower licence |
| Responsible actor | No one | ELY + MMM + Russia | Kemijoki Oy + ELY |
| Drought response mechanism | Absent — no legal pathway | Treaty-constrained juoksutussääntö | Licence conditions + market dispatch |
| Objective function | N/A | Level stability + flood/drought prevention | Electricity production |
| HEPP function | Document absent mechanism | Document pace vs. treaty trigger speed | Monitor ecological endurance vs. production optimisation |
| Correction gap character | Structural absence | Undersized instrument | Misaligned objective |
The spring 2026 drought affected all three system types simultaneously — the same meteorological driver, three fundamentally different institutional responses. This is the empirical basis for HEM's comparative function: the instrument does not prescribe what should be done differently, but it makes visible how different regulatory architectures translate the same hydrological stress into different observable outcomes.
§ 09The summer 2026 hydrological situation — characterised by below-average snow cover, early melt, and persistent multi-year deficit in eastern and northern Finland — offers a rare natural experiment. The same physical driver (accumulated moisture deficit since summer 2024, compounded by the low-snow winter of 2025–2026) propagated through four structurally different institutional architectures simultaneously.
Virmasvesi (Rautalammin reitti — unregulated): No institutional response was available. The protected free-flowing status of the route that gives it high ecological value simultaneously removes the legal infrastructure through which corrective water management could operate. The endurance deficit accumulated without triggering any institutional process. HEPP's function here is documentary: it creates the record of a deficit that the institutional system has no language for.
Saimaa (treaty-constrained): The mechanism activated — correctly and at the right time. But it reached its treaty floor before the deficit reached its projected maximum. The instrument and the problem are proportioned differently: the treaty was designed for single-season anomalies, not two-year cumulative deficits compounded by structural snow decline. HEPP here documents the mismatch between instrument design envelope and emerging climate envelope.
Kallavesi / Vuoksen latva (hydropower licence): Regulated lakes managed by Savon Voima and others responded within their licence conditions. The spring drawdown (kevätkuoppa) requirement in some licences created additional stress when low snow meant the drawdown preceded a recharge pulse that never arrived. Licence modification pathways exist (vesilaki §18:3a) but are slow — designed for deliberate policy revision, not seasonal response. HEPP here documents the lag between climate-driven licence obsolescence and the pace of administrative adaptation.
Kemijoki / Oulujoki (full power regulation): Maximum operational flexibility, but the objective function is electricity not ecology. Reservoir drawdown for power production during high-price winter periods reduces the buffer available for the following spring. HEPP here would need to integrate production dispatch data alongside hydrological measurements — a coupling not yet implemented but technically feasible given available Fingrid data series.
The pattern across all four architectures is consistent with SP-007's core claim: the institutional response in each case is biologically and structurally rational given the framework within which the actors operate. No one made an error. The errors are architectural — built into the frameworks decades before the current climate trajectory was observable. HEM does not resolve these architectural misalignments. It makes them legible.
For Virmasvesi specifically: the low summer water level that you observe from the lake shore is not the result of inaction by an identifiable decision-maker. It is the result of a regulatory architecture designed in a different climate — one where a protected free-flowing route and a low-snow winter were not expected to coincide at this frequency. The endurance deficit is real. The institutional gap is real. The instrument for making both visible is what HEM is for.
§ 10An informed external reviewer made three observations that sharpen the analysis and one methodological point that requires clarification. All four are worth documenting here because they reflect the kind of institutional dialogue that TN-014 is designed to generate.
The reviewer correctly identifies the risk of conflating three different things: what data shows, what it implies hydrologically, and what it implies institutionally or politically. This is a real risk in any composite index. HEPP is not immune to it. The HSP component measures how many consecutive weeks water level has remained below 90% of the rolling mean — this is a hydrological observation. The interpretation that this constitutes an institutional failure is a separate, normative claim that requires additional premises. TN-014 attempts to keep these layers distinct but the distinction is easier to state than to maintain in practice. The reviewer's framing — riskikommunikaation työkalu rather than totuusmittari — captures the appropriate epistemic status precisely.
The reviewer notes that unregulated watercourses often have significant ecological values: continuity, fish populations, natural sediment dynamics, and resistance to single-objective optimisation failures. This is an important corrective to any reading of TN-014 that implies regulation is straightforwardly better. The argument here is not that the Rautalammin reitti should be regulated. It is that the conditions under which its unregulated status was chosen — a climate in which low-snow winters at the current frequency were rare — are changing. As the reviewer puts it: säätelemättömyys ei enää tarkoita historiallista luonnontilaa. The preferred institutional response — a tilapäinen kuivuusprotokolla with a very high activation threshold rather than permanent heavy regulation — is structurally compatible with the ACI analysis.
The reviewer proposes a realistic institutional entry sequence: open methodology → documented case examples → retrospective validation → institutional interest. This matches ACI's actual production order. TN-014 is the case example. ERA5-Land retrospective analysis of the 2024–2026 deficit period constitutes the validation step. The institutional interest, if it materialises, follows from that. The reviewer is right that direct entry into official monitoring systems is not the realistic near-term path. The realistic path is demonstrated credibility through open, replicable methods.
The reviewer notes that a momentary inflow/outflow deficit does not by itself indicate a system error — and is correct. But this is precisely the distinction that the HSP (Hydrological Stress Persistence) component of HEPP is designed to capture. A single day of outflow exceeding inflow is hydrologically unremarkable. HSP measures the duration: how many consecutive weeks has the level remained below 90% of the rolling seasonal mean. The HEPP signal becomes significant not when the deficit appears but when it persists. In the Virmasvesi case, the persistence began in autumn 2025 and has continued through spring 2026 — approximately 26–30 consecutive weeks. That duration, not the instantaneous flow balance, is what HEPP quantifies. The momentary signal and the endurance signal are different instruments measuring different things.
Integrating the external commentary, HEM's institutional function is most accurately described as follows: HEPP is a persistence-weighted stress index designed to make accumulating hydrological deficits legible before conventional threshold monitoring registers them as anomalous. It does not predict water levels, prescribe regulatory responses, or resolve the normative question of how unregulated versus regulated systems should be governed under changing climate conditions. It creates a time-stamped, replicable record of when endurance conditions crossed interpretive thresholds — and makes that record available to the actors who do have authority to respond.
The paradigm shift the reviewer identifies — from maximising a single utility to minimising systemic fragility — is the analytical frame within which HEPP becomes interesting. That shift has not yet occurred in Finnish water resource governance. Whether it will, and on what timeline, is not a question HEM can answer. It can only document the conditions under which the question becomes unavoidable.
A second round of external commentary identifies two gaps in the current analysis that are worth addressing directly: the term "hydrological endurance failure" requires an explicit baseline, and the paper's underlying causal logic should be stated as a formal chain rather than left implicit across sections.
The critic is right that "failure" without a specified reference invites the rebuttal: the lake is not failing, it is simply low. This is a legitimate objection. HEM uses "endurance failure" in a specific technical sense that must be stated explicitly.
Hydrological endurance failure is defined here as: a sustained reduction in the functional capacity of a lake or river system, where "functional capacity" is assessed across five reference domains simultaneously:
| Domain | Failure condition | Timescale |
|---|---|---|
| Ecological continuity | Littoral habitat compression; thermal stratification disruption; spawning access loss | Weeks–season |
| Groundwater recharge | Lateral recharge gradient reversed or eliminated; well levels declining | Weeks–months |
| Navigation and infrastructure | Docks, intake structures, or channels below operational minimum depth | Immediate |
| Water supply security | Municipal or agricultural intake approaching or below design minimum | Weeks–months |
| Resilience buffer | Available storage below the level that would allow absorption of a subsequent drought event without crossing ecological or operational minima | Season–year |
Endurance failure is not any single domain threshold being crossed. It is the persistent simultaneous depression of functional capacity across multiple domains — which is what HEPP attempts to index. A lake that is low for three days in August is not in endurance failure. A lake that has been below 90% of its seasonal norm for 26 consecutive weeks, with groundwater levels declining and dock access compromised, is. The distinction is temporal integration, not instantaneous exceedance.
The paper's argument is distributed across nine sections. Stated as a formal causal chain, it runs:
Meteorological stress (low snow accumulation, early melt, precipitation deficit, elevated evaporation) →
Hydrological persistence (inflow remains below seasonal baseline for extended consecutive period; recharge pulse absent or attenuated) →
Endurance deficit accumulation (storage declining across multiple reference domains; HEPP rising above 0.50 threshold) →
Institutional translation failure (regulatory framework lacks mechanism to translate endurance signal into decision prompt; no actor holds activation authority for the specific deficit type) →
Delayed or absent correction (intervention window closes; low-cost actions unavailable by the time conventional thresholds register anomaly) →
Visible functional degradation (observable consequences at lake shore: dock access, groundwater levels, water quality, ecological indicators) →
Post-hoc attribution (consequences attributed to weather or drought rather than to the institutional translation gap, foreclosing institutional learning).
HEM intervenes at step three — between endurance deficit accumulation and institutional translation failure. It does not resolve the translation failure. It creates a time-stamped, publicly accessible record of when the deficit crossed interpretive thresholds, making the translation gap visible rather than invisible. Whether that visibility produces an institutional response depends on factors outside HEM's scope.
The commentary identifies three directions for future development that are acknowledged but not addressed in this version. First, calibration: the current HEPP weights (SD 0.40, HSP 0.35, RF 0.25) are conceptually motivated but not empirically validated. Retrospective hindcast analysis of the 2024–2026 deficit period against SYKE observational records would constitute the first calibration step. Second, sensitivity analysis: how sensitive are HEPP readings to weight perturbations, and under what parameterisations do false positive rates become problematic? Third, the energy-water nexus: the Kemijoki discussion in §08 opens the observation that reservoir drawdown for electricity dispatch is part of the hydrological stress system. Integrating Fingrid production data with basin-level hydrology would extend HEM into genuinely novel territory — a direction flagged for a future technical note.