Abstract
Identification of drought is essential for many environmental and agricultural applications. To further understand drought, this study presented spatial and temporal variations of drought based on satellite derived Vegetation Condition Index (VCI) on annual (Jan–Dec), seasonal monsoon (Jun–Nov) and pre-monsoon (Mar–May) scales from 1982–2015 in Nepal. The Vegetation Condition Index (VCI) obtained from NOAA, AVHRR (National Oceanic and Atmospheric Administration, Advanced Very High Resolution Radiometer) and climate data from meteorological stations were used. VCI was used to grade the drought, and the Mann–Kendall test and linear trend analysis were conducted to examine drought trends and the Pearson correlation between VCI and climatic factors (i.e., temperature and precipitation) was also acquired. The results identified that severe drought was identified in 1982, 1984, 1985 and 2000 on all time scales. However, VCI has increased at the rate of 1.14 yr−1 (p = 0.04), 1.31 yr−1 (p = 0.03) and 0.77 yr−1 (p = 0.77) on the annual, seasonal monsoon and pre-monsoon scales, respectively. These increased VCIs indicated decreases in drought. However, spatially, increased trends of drought were also found in some regions in Nepal. For instance, northern areas mainly in the Trans-Himalayan regions identified severe drought. The foothills and the lowlands of Terai (southern Nepal) experienced normal VCI, i.e., no drought. Similarly, the Anomaly Vegetation Condition Index (AVCI) was mostly negative before 2000 which indicated deficient soil moisture. The exceedance probability analysis results on the annual time scale showed that there was a 20% chance of occurring severe drought (VCI ≤ 35%) and a 35% chance of occurring normal drought (35% ≤ VCI ≤ 50%) in Nepal. Drought was also linked with climates in which temperature on the annual and seasonal monsoon scales was significant and positively correlated with VCI. Drought occurrence and trends in Nepal need to be further studied for comprehensive information and understanding.
Highlights
Drought is a serious phenomenon and ranks first among all natural hazards in terms of the number of people affected globally [1]
The Vegetation Condition Index (VCI) during the seasonal monsoon and pre-monsoon season increased at the rate of 1.31 yr−1 and 0.77 yr−1, respectively
This study investigated spatial and temporal variation of droughts based on satellite derived
Summary
Drought is a serious phenomenon and ranks first among all natural hazards in terms of the number of people affected globally [1]. Drought hazards increase slowly, which often accumulate over. Sensors 2019, 19, 430 a considerable period and may linger for years after termination [2]. It has been recognized as one of the sensitive environmental disasters affecting natural ecosystem, agriculture and hydrological systems [3]. As the onset and end of drought are difficult to determine, the drought severity is sometimes incredibly difficult to quantify. Droughts appear as a condition of below average rainfall and slowly develop as an extreme climatic event that has severe impacts on the environment [4].
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