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About this monitor
Flash drought definition. A flash drought is identified from the pentad (5-day) root-zone soil-moisture percentile: the percentile falls from above the 40th to at or below the 20th within six pentads (about a month), stays at or below the 40th percentile for 4–30 pentads with at least two pentads at or below the 20th, and ends when the percentile recovers above the 40th. A slower decline — typically taking more than about nine pentads (1.5 months) to reach the 20th — falls to the conventional-drought rule instead.
Steps used to identify each event (Development → Propagation → Recovery, after Mahto & Mishra, 2023):
- Candidate onset. Find the most recent pentad with SM percentile above the 40th — the last "normal" pentad before a possible drought.
- Development phase. Within the next 6 pentads (about a month), the percentile must fall to the 20th percentile or below, without climbing back above the 40th in between.
- Propagation phase. The event must reach the 20th percentile or below on at least 2 pentads, with the pentad right after the first of these at or below the 25th, and must run for 4–30 pentads in total.
- Recovery (termination). The event ends at the first pentad where the percentile climbs back above the 40th.
- Peak. The lowest percentile reached anywhere between onset and recovery, and the pentad it occurred in, are recorded as Peak_SMpercentile and Peak_SMpentad.
Phase framework after Mahto & Mishra (2023, Environmental Research Letters); this version uses the 40th percentile for recovery, matching the scripts behind this portal.
Status classes. Checked in this order; the first match wins. Ongoing flash drought: the rapid-onset rule above, applied live, with no recovery yet. Ongoing conventional drought: today's percentile is below the 20th; of the 15 preceding pentads (about 75 days), at most one may exceed the 40th and the rest must stay below it, with their average below the 30th — a persistent, slower-moving drought that doesn't fit the flash pattern (often a flash drought that has run past the 30-pentad cap above). Its onset is the last pentad before that 15-pentad window that was above the 40th. Developing (watch): a short-lead forecast signal, not a persistence test — the district was normal (above the 40th) one or two pentads ago, is now below the 40th, and the rainfall-forecast-driven soil-moisture prediction has it falling below the 20th over the next two pentads while still declining. No active drought: none of the above; the map can show the days since the last flash-drought event ended.
Dates. “Started” is the start date of the onset pentad (the last pentad above the 40th percentile before the drop). “Ended” is the start date of the first pentad back above the 40th percentile. Pentads begin on 1 January in 5-day steps (73 per year).
Data. District means of root-zone (0–100 cm) soil moisture, converted to percentiles against the 1981–present record for the same time of year (pooling ±1 pentad). The most recent days rely on soil moisture predicted from IMERG and ECMWF forecast rainfall, so the latest status can change as observations arrive.
Trend and severity history. The area-under-drought trend below the map plots the flash and conventional definitions independently — each computed on its own terms and weighted by district area rather than district count, so they can overlap. The severity-history chart further down uses the same D0–D4 dry percentile classes as the map's severity layer (it tracks the dry side only, not the W0–W4 wet classes or Normal), plotted cumulatively (each colour is the area at or beyond that class) for the current calendar year to date, the same way the U.S. Drought Monitor presents its percent-area chart.
Severity classes (D4–W4). The “Current severity” map layer classes every district by today's soil-moisture percentile alone, independent of flash-drought status, across the full dry-to-wet spectrum:
| Class | Percentile | Colour |
|---|---|---|
| W0 – Abnormally wet | ≥ 70 | Pale blue |
| W1 – Moderate wet | ≥ 80 | Light blue |
| W2 – Severe wet | ≥ 90 | Blue |
| W3 – Extreme wet | ≥ 95 | Deep blue |
| W4 – Exceptional wet | ≥ 98 | Navy |
| Normal | 30 – 70 | Pale green |
| D0 – Abnormally dry | ≤ 30 | Yellow |
| D1 – Moderate dry | ≤ 20 | Tan |
| D2 – Severe dry | ≤ 10 | Orange |
| D3 – Extreme dry | ≤ 5 | Red |
| D4 – Exceptional dry | ≤ 2 | Dark red |
| No data | — | Gray |
The D0–D4 dry classes, their percentile thresholds and colour scheme follow the U.S. Drought Monitor, adapted here to root-zone soil-moisture percentile for Indian districts. The W0–W4 wet classes mirror the same thresholds on the wet side of the distribution. “Normal” and “No data” use colours of our own choosing so they stay visually distinct on this map.