Thailand Reservoir Transparency

For the COVERED subset (35 large dams tracked by ThaiWater/RID plus EGAT's 9 major hydropower reservoirs), publication is consistent: daily storage in million m³, fill percentages, inflow/outflow. RID Water Report Portal publishes daily situation reports. EGAT publishes monthly statistics for 9 hydropower dams. The typical covered reservoir has daily updates in structured HTML and downloadable bulletins. The main weakness is EGAT data being monthly rather than daily for the country's highest-capacity dams.

For the COVERED subset, the dominant access mechanism is a documented public REST API operated by RID (app.rid.go.th/reservoir/api/) with current and date-parameterised historical endpoints returning JSON. The API was observed returning PHP errors during testing (Array to string conversion), indicating reliability issues. A water data exchange standard (standard.thaiwater.net) defines RESTful API specifications but is Thai-only. EGAT offers HTML tables only. ThaiWater provides interactive dashboards but no official public API endpoint. More advanced than SEA peers but falls short of a clean, stable, authenticated REST API.

Methodology v1.3.0 (capacity-weighted), conservative denominator. Reported Thai national reservoir storage capacity per RID+EGAT is approximately 75,000 hm³, dominated by EGAT's 9 major hydropower reservoirs — Srinagarind (17,745 hm³), Bhumibol (13,462 hm³), Sirikit (9,510 hm³), Vajiralongkorn (8,860 hm³), Rajjaprabha (5,639 hm³), Ubol Ratana, Sirindhorn, Pak Mun, Chulabhorn — plus RID's main large reservoirs (Pasak Jolasid, Khun Dan Prakarn Chon, Lam Pao, Mae Kuang, Mae Ngat, Kiu Lom, Krasiao, Bang Lang). Applying a +10% conservative uplift to account for the long tail of provincial RID medium-scale and small-scale reservoirs (>1,000 ang khep nam dataset), agricultural Land Development Department impoundments, private estate reservoirs serving industrial estates and aquaculture, and military-administered reservoirs not in the public dam doluluk panel, the realistic denominator is approximately 82,500 hm³. Covered capacity through ThaiWater + RID API (35 large RID dams with daily storage) plus EGAT monthly bulletins (9 hydropower dams) totals approximately 60,000 hm³. Coverage = round(100 × 60,000 / 82,500) = 72. The residual gap is the bulk of medium and small RID reservoirs that appear in occasional bulletins but not the routine API panel, plus agricultural reservoirs of regional importance never published nationally.

MEDIAN historical depth across the 35 covered reservoirs is approximately 10-15 years. Researchers for the MSEA-Res academic dataset (2025, ESSD) successfully downloaded daily storage data for 20 Thai reservoirs from ThaiWater's National Water Database, confirming programmatic historical access back roughly 10-12 years. The RID API date-parameterised endpoint has at least 2022 confirmed. ThaiWater annual reports go back to 2021 publicly. No continuous public daily dataset back to the 1990s. Band: median 10-20 years.

For the COVERED subset, the typical cadence is DAILY: RID Water Report Portal and ThaiWater publish daily reservoir situation reports, with ONWR national water reports timestamped to 7am. The RID reservoir database provides daily and monthly records. EGAT's 9 hydropower dams update monthly. Weekly English-language water watch PDFs supplement. Daily for the most important national aggregates is strong by regional standards.

For the COVERED subset, capacities are published on individual EGAT dam pages (e.g. Bhumibol 13,462 Mm³, Sirikit 9,510 Mm³) and in the RID database schema. ThaiWater annual reports reference rainfall estimation via Inverse Distance Weighting and aggregate storage methodology, but do not describe how in-situ storage readings are taken — telemetry instrumentation, stage-storage curve derivation, or sedimentation correction methods are not published. The Mekong Dam Monitor methodology page notes use of ALOS DEM-derived hypsometric look-up tables, but this is a third-party reconstruction. The absence of a public technical metadata file with stage-storage curves or measurement uncertainty limits this dimension.

Thailand stands out in the region for meaningful English-language access. EGAT maintains a full English website. RID has an English-language portal and publishes weekly English water watch PDFs. HII's website is fully bilingual. ThaiWater has an English-language URL for the dam report page. However, the RID reservoir database and API documentation, the standard.thaiwater.net API portal, and most detailed operational data portals are Thai-only. English is strong for headlines but weak for technical and programmatic access.