Monitoring hydrological drought using a newly developed MODIS reservoir product

Reservoirs are most commonly used for coping with drought and water shortages. However, reservoirs also suffer from low water storage and excessive evaporative losses. Therefore, hydrological drought quantification using reservoir information is essential for water management. However, in-situ data about reservoir storage and evaporation loss have been lacking at a large scale. We introduce a framework for monitoring hydrological droughts using a Moderate Resolution Imaging Spectroradiometer (MODIS) based new reservoir product (MOD28). This MODIS product contains reservoir data at two temporal resolutions for 164 reservoirs (44% of global capacity) since 2000. The first one provides the 8-day storage, elevation, and area values. The second one includes monthly storage, elevation, area, evaporation rate, and evaporation volume values. In addition, the reservoir storage drought index (RSDI) is calculated as the 8-day normalized reservoir storage time series. The RSDI can be further used to characterize drought severity, duration, and recovery time. It also helps to characterize drought propagation from meteorological and agricultural droughts into hydrological droughts. By comparing the ratios between evaporation volume and storage volume (monthly) during drought events with those during the periods without droughts, a better understanding about the effects of reservoir evaporation on water resilience can be achieved. In this presentation, we will first introduce the new MODIS data product, then show examples of reservoirs under hydrological drought conditions across representative global locations. Results suggest that both the storage and evaporation estimates from MODIS are in agreement with in situ observations. With a temporal resolution higher than most other drought indices, the RSDI uniquely benefits the characterization of drought propagation. Moreover, this index improves the capability for near real-time drought monitoring to support decision-makers in local drought assessment. This new reservoir-based monitoring framework is the first to evaluate drought impacts by considering both storage shortages and evaporation loss. The long term (20 years) high quality remote sensing data also allow us to investigate drought from a climatological perspective.