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Drought is a intermittent natural hazard having a critical socio-economic and environmental effect (Asadi Zarch et al., 2015). The United Nations declared this menacing creeping phenomenon as one of the deadliest natural disasters. It affects almost every climatic zone, however, the adverse effects on the ecology and human society may vary spatially (Haroon et al., 2016). It is estimated that nearly more than 50% of the terrestrial earth is susceptible to drought each year. The productive lands of all continents lose millions of tones of agricultural production annually because of this recurring phenomenon.
The ruthlessness of drought depends upon the extent of the affected area, and related impacts of human activities, agriculture, and the environment (Caparrini and Manzella, 2009). Contrasted with other natural hazards, drought is more difficult to scrutinize as the commencement and conclusion of a specific dry spell is hard to resolve. The impacts can be underestimated until they reach peak intensities. The social, physical, and economic impacts of droughts can be staggering especially in developing countries; its immediate consequences include shortages in water supply, destruction of ecological resources and damage to agricultural production, resulting in famine, human suffering, casualties and regional abandonments (Kogan, 1997). Therefore, assessing drought is of great importance as it is viewed as the most severe problem in most countries in terms of food security and socio-economic stability (Fang et al., 2019; Hazaymeh and Hassan, 2017). Damage mitigation caused by drought demands an adequate water resource planning that can be effectively accomplished only if routine monitoring of drought has been carried on. Thus, the term drought monitoring refers to the simultaneous evaluation of all possible causes and consequences on the soil-vegetation system (Caparrini and Manzella, 2009).
The traditional methods of assessing and monitoring drought rely upon rainfall data from meteorological observation stations. However, these data are limited in a region, often inaccurate and difficult to gather in near-real-time (Thenkabail et al., 2004). On the other hand, satellite data are consistently available and can be used to detect the onset, duration, and severity of the drought. Initially, synoptic monitoring of drought started with NOAA AVHRR (Advanced Very High-Resolution Radiometer) data (Kogan, 2000). However, because of its coarse resolution (10 Km), it can be hardly used in monitoring drought at large scales (a district or village). Subsequently, it has been successfully replaced by MODIS (Moderate Resolution Imaging Spectroradiometer) data. The time-series MODIS image provides near-real-time, continuous and relatively high-resolution data. This helps to assess the development of drought and its severity in regions with limited and inaccurate ground meteorological observations especially in South-East Asia including India (Thenkabail et al., 2004). The Vegetation Health Index (VHI) approach is proved to be one of the most widely accepted remote sensing-based drought assessment approaches. The index successfully captures the onset, duration, cessation, frequency, and severity of drought (Gidey et al., 2018). However, if high-resolution images are available at a regular interval, then Normalized Multiband Drought Index (NMDI) (Wang and Qu, 2007) and Normalized Difference Drought Index (NDDI) (Gu et al., 2007) may yield interesting results.
Soil erosion is the cornerstone in the sedimentation process, a combined process of erosion, transportation, and deposition of sediments. Soil erosion is the result of complex processes controlled by climate, terrain and land-use / landcover characteristics of that area. It is regarded as the major and most widespread kind of soil degradation, which significantly affects the sustainable agricultural land-use (Kouli et al., 2009). Soil erosion is directly related to the soil surface and the volume of disturbed soil. Its spatial distribution pattern is related to the soil and water conservation measures and plays a crucial role in studying erosion and sinks (Shinde et al., 2011). Intensive agricultural practices govern soil characteristics, specifically in steep-slope areas (Quine and Zhang, 2002).
However, it is a gradual process of detachment and removal of soil particles by water causing soil degradation (Shao-Xiang et al., 2004). Soil erosion causes manifold problems such as loss of soil nutrients, reduction of crop yields and productivity (Renard et al., 1997). Eroded soils carry valuable nutrients and harmful pesticides and chemicals into rivers, streams and groundwater resources. The erodibility is accelerated rapidly due to direct and indirect anthropogenic activities like mining, querying, expansion of settlements and other civil constructions and agricultural practices (Islam et al., 2018). It is reported that the erosion is typically higher in cultivated land than that of the uncultivated land (Brown, 1984).
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