Climate change impacts on spatio-temporal soil water extremes in geophysically diverse watersheds: A comparison between east and west Tennessee watersheds

Authors: SAHA, PROBAL - University Of Tennessee; HATHAWAY, J - University Of Tennessee; SCHWARTZ, J - University Of Tennessee; WILSON, C - University Of Tennessee; ABBAN, B - Us Bureau Of Reclamation; Papanicolaou, Athanasios - Thanos

Submitted to: Journal Hydrologic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Predicted future increases in temperature of 2.7-6.4°C and extreme precipitation events, damping large water volumes within hours that are usually encountered collectively over a period of a year or years, will have a significant impact on crop production and suggest a potential shift in growing seasons by nearly a month earlier in the US Southeast. Furthermore, due to increasing temperature the average soil moisture will be decreasing, with the predicted ranges of monthly maximum and minimum values suggesting a substantial number of extreme soil moisture values below the average wilting point. This will have significant implications to rainfed production with anticipated reduction in yields. In fact, during 2046-55, a 34-46% of the growing season for Tennessee is predicted to be below the average wilting point, highlighting the need for irrigation or the use of water-efficient crops. It is also observed that the available water in soil before irrigation reduces significantly faster for future scenarios due to enhanced evaporation, indicating a 60% increase in irrigation demand for the major crops of Tennessee. This information produced in this study has significant implications on water availability for agricultural activities in the US Southeast. The broader implication of the study for land managers would be implementing an effective management plan to increase the organic matter content in croplands, which has the potential to significantly reduce irrigation requirements during water scarcity in the future. Therefore, it is essential to conduct an analysis of water-efficient crops and organic matter management techniques for extreme climate scenarios.

Technical Abstract: Climate change impacts hydrologic processes, compelling more regional water budget studies to understand spatio-temporal hydrological extremes. This study investigates the effects of climate change on water budgets, with a focus on soil moisture, in two Tennessee watersheds with different geo-climatic characteristics, Obion and Nolichucky Rivers. Using the hydrological model VIC, the study projects water budgets for these watersheds until 2099, analyzing annual and seasonal runoff, recharge, and soil moisture to identify trends and extremes. Results show that an increase in temperature of 2.7-6.4°C and a change of precipitation by 1-4% is predicted for Tennessee, which will impact seasonal patterns, water balances, and soil moisture regimes. The overlapping of such impacts can lower soil moisture below the wilting point during 40-50% of the growing season, impacting crop yields. The study identifies field capacity, clay soil percentage, and organic matter as key factors impacting the spatial extremes of croplands' irrigation requirements. These findings underscore the need to understand soil moisture variability and extreme soil water conditions to optimize soil-water management scenarios and mitigate future water shortage risks.