Discussion of “Multivariate Modeling of Projected Drought Frequency and Hazard over India” by Vivek Gupta, Manoj Kumar Jain, and Vijay P. Singh

Abstract

Drought is one of the most damaging natural disasters that affect agriculture, water resources, economy, and socioeconomic conditions. Therefore, understanding the occurrence and drivers of droughts in India under the observed and projected future climate remains essential. Notwithstanding the importance of understanding droughts in the observed and projected future climate in India, there remain some challenges. Because drought has several classifications (meteorological, hydrological, agricultural, and socioeconomic), the variables used to identify and evaluate the impacts of droughts are numerous. Therefore, there can be a debate on the importance of hydrological (evapotranspiration, streamflow, and soil moisture) and climate [precipitation, vapor pressure deficit, and potential evapotranspiration (PET)] indicators to identify droughts (Mishra and Singh 2010; Shah and Mishra 2015, 2019). Nonetheless, drought indicators such as the Standardized Precipitation Index (SPI) (Mckee et al. 1993) and Standardized Precipitation Evapotranspiration Index (SPEI) (Vicente-Serrano et al. 2010) are widely used due to the availability of required data sets and the simplicity in their estimation. SPEI arguably has an advantage over SPI because it considers the role of temperature on drought (Vicente-Serrano et al. 2010). Considering the role of temperature on drought under the warming climate is important to employ atmospheric water demands (PET) in the drought estimation. Therefore, SPEI is based on the difference between precipitation (P) and PET over a period of time. The original paper estimated the drought frequency and hazard over India under the projected future climate. While the authors did a thorough analysis to determine the frequency of drought in different regions of India, the assessment has the potential for improvement and raises some obvious questions. The estimation of PET, which is required for SPEI under the warming climate, is challenging and therefore widely discussed in the published literature (Dai 2011b; Hobbins et al. 2008; Sheffield et al. 2012). The original paper used the Thornthwaite method (PET-TH) (Thornthwaite 1948) to estimate PET for the historical and projected future climate , assuming that atmospheric water demands (PET) in the future will be largely driven by temperature.