Understanding spatio-temporal dynamics in soil moisture and groundwater in a Critical Zone Observatory (CZO) in Ganga basin, North India

Abstract:

Soil moisture poses a crucial control on the Earth’s surface-atmosphere interactions and plays an active role in hydrological cycle. Simultaneous measurement of surface soil moisture and groundwater level can help to understand the complex interaction between near surface and deeper hydrology regime that is particularly crucial for the assessment of agriculture water requirements. Here, we investigate the spatio-temporal dynamics of surface soil moisture and depth to groundwater table (DTGT) in an agriculture-dominated critical zone observatory (CZO) in Ganga basin in northern India. Field based campaign were conducted for both the measurements using a handheld ML3 ThetaProbe and WaterScout SM100 sensors (soil moisture measurements) and the water level recorder (DTGT measurements). A total of 21 soil moisture and 58 open wells were monitored from September, 2017 to December, 2019. Along with the soil moisture and DTGT, the observed variation in daily rainfall was measured from the in-situ weather stations. Statistical and temporal stability analyses were carried out to compute the mean spatial variability and the number of optimal sampling sites on both the datasets. The spatial soil moisture variability was found to be low (0.05) during wet period, and fairly high (0.68) during dry period. Similarly, spatial variability of DTGT ranges from 0.2-0.6 for dry and wet period respectively. Result on the temporal stability analysis shows that four most representative sites can reproduce CZO mean soil moisture with an accuracy of ±3%. Furthermore, five stable open wells are identified for groundwater monitoring which can provide the mean groundwater table depth for the CZO with a determination coefficient, R², equal to 0.98. Although, natural causes are considered to depict the spatio-temporal dynamics, inputs from local community has to be incorporated for minimizing the resultant anomaly.