Monitoring Residual Soil Moisture and Its Association to the Long-Term Variability of Rainfall over the Upper Blue Nile Basin in Ethiopia

Authors

Getachew Ayehu, Ethiopian Space Science & Technology Institute & Bahir Dar UniversityFollow
Tsegaye Tadesse, University of Nebraska - LincolnFollow
Berhan Gessesse, Ethiopian Space Science & Technology InstituteFollow

ORCID IDs

Getachew Ayehu https://orcid.org/0000-0001-8060-9227

Tsegaye Tadesse https://orcid.org/0000-0002-4102-1137

Berhan Gessesse https://orcid.org/0000-0001-7568-8178

Document Type

Article

Date of this Version

7-3-2020

Citation

Remote Sens. 2020, 12, 2138;

doi:10.3390/rs12132138

Comments

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license

Abstract

Monitoring soil moisture and its association with rainfall variability is important to comprehend the hydrological processes and to set proper agricultural water use management to maximize crop growth and productivity. In this study, the European Space Agency’s Climate Change Initiative (ESA CCI) soil moisture product was applied to assess the dynamics of residual soil moisture in autumn (September to November) and its response to the long-term variability of rainfall in the Upper Blue Nile Basin (UBNB) of Ethiopia from 1992 to 2017. The basin was found to have autumn soil moisture (ASM) ranging from 0.09–0.38 m³/m³, with an average of 0.26 m³/m³. The ASM time series resulted in the coe_cient of variation (CV) ranging from 2.8%–28% and classified as low-to-medium variability. In general, the monotonic trend analysis for ASM revealed that the UBNB had experienced a wetting trend for the past 26 years (1992–2017) at a rate of 0.00024 m³/m³ per year. A significant wetting trend ranging from 0.001 to 0.006 m³/m³ per year for the autumn season was found. This trend was mainly showed across the northwest region of the basin and covers about 18% of the total basin area. The spatial patterns and variability of rainfall and ASM were also found to be similar, which implies the strong relationship between rainfall and soil moisture in autumn. The spring and autumn season rainfall explained a considerable portion of ASM in the basin. The analyses also signified that the rainfall amount and distribution impacted by the topography and land cover classes of the basin showed a significant influence on the characteristics of the ASM. Further, the result verified that the behavior of ASM could be controlled by the loss of soil moisture through evapotranspiration and the gain from rainfall, although changes in rainfall were found to be the primary driver of ASM variability over the UBNB.