Abstract
A new index for agricultural drought monitoring is presented based on the integration of different soil/vegetation remote sensing observations. The synergistic fusion of the surface soil moisture (SSM) from the Soil Moisture and Ocean Salinity (SMOS) mission, with the Moderate Resolution Imaging Spectroradiometer (MODIS) derived land surface temperature (LST), and water/vegetation indices for agricultural drought monitoring was tested. The rationale of the approach is based on the inverse relationship between LST, vegetation condition and soil moisture content. Thus, the proposed Soil Moisture Agricultural Drought Index (SMADI) combines the soil and temperature conditions while including the lagged response of vegetation. SMADI was retrieved every eight days at 500 m spatial resolution for the whole Iberian Peninsula (IP) from 2010 to 2014, and a time lag of eight days was used to account for the plant response to the varying soil/climatic conditions. The results of SMADI compared well with other agricultural indices in a semiarid area in the Duero basin, in Spain, and also with a climatic index in areas of the Iberian Peninsula under contrasted climatic conditions. Based on a standard classification of drought severity, the proposed index allowed for a coherent description of the drought conditions of the IP during the study period.
Highlights
Most drought definitions [1,2,3,4] rely on its area of impact
Since the temperature behavior is opposite to the Normalized Difference Vegetation Index (NDVI), the form of the Equation (6) differs from Equation (5), in order to equals the meaning of the condition index, in which low values represented dry conditions, whereas high values represented wet or no stressed conditions
We propose five drought categories relying in the merged legend between the categories found in research alike [64,66,69,70], all of them based in turn in Vegetation Condition Index (VCI), Temperature Condition Index (TCI) or other NDVI-Normalized Difference Water Index (NDWI)-based proxies, i.e., non-drought, abnormally dry, moderate drought, severe drought and extreme drought (Table 4)
Summary
Most drought definitions [1,2,3,4] rely on its area of impact. Broadly, an agricultural drought refers to soil water deficit, whereas a meteorological drought is characterized by a prolonged and abnormal deficiency of precipitation. Socioeconomic drought is related to the surplus of demand of economic goods as a result of a weather-related shortfall in water supply that affects population Another emerging definition that is gaining widespread use in recent years is flash drought, defined as a severe, short-term event characterized by soil moisture deficit and abnormally high temperatures, negatively impacting vegetation conditions [5,6]. Agricultural drought does not begin with the rain decrease, but rather when available stored water supports actual evapotranspiration at only a small fraction of the potential evapotranspiration rate [33] In this regard, an agricultural drought index should integrate various parameters like rainfall, temperature, evapotranspiration, runoff, and other water supply indicators that impact crop growth and development during drought episodes into a single number [34]. Different categories of agricultural drought are suggested based on the proposed index
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