Abstract:
Agriculture is the main field of the economy that brings profit to Sri Lanka, and Sri
Lanka is also considered as the grain storage of South Asia. Sri Lankan agriculture
mainly depends on crops like paddy, tea, etc. Therefore, it is vital to identify the
problems that can cause damage to the field of agriculture. One such problem is
agricultural droughts, which are caused by the shortage of water for agricultural
purposes. There have been many indices developed for the monitoring of the
phenomena related to the agricultural fields in remote sensing. This research is mainly
focused on monitoring agricultural droughts with the use of soil moisture and some
selected vegetation indices that were derived from Landsat multispectral data. It has
chosen the Soil Moisture Index (SMI) and some vegetation indices that have an
influence to the growth of plants. SMI was computed using the relationship between
the Normalized Difference Vegetation Index (NDVI) and the Land Surface
Temperature (LST) and can measure the soil moisture of the top layer of soil. SMI
and the Delta index values were compared with the Standardized Precipitation Index
(SPI) values taken from the Department of Meteorology Sri Lanka, which have been
currently used for drought monitoring purposes. Both indices showed different
correlations with the SPI values, and SMI showed the highest correlation of 0.39 with
the SPI – 1-month data of the study area. Then with the vegetation indices, SMI
showed high correlation with Land Surface Water Index (LSWI) than the Enhanced
Vegetation Index (EVI) and the Soil Adjusted Water Index (SAVI). The regression
model between the vegetation indices and the SMI gave the R squared value of 0.63.
And the regression model also emphasizes that the SMI shows a high correlation with
the LSWI index in the North Central Province, as the regression coefficient for that
index was higher than others. Hence, it was evident that soil moisture alone cannot be
used for agricultural drought monitoring, and there are other parameters that can affect
crop production.
