Exploring relationships between precipitation, soil moisture, and extreme temperature events in observations and climate models

Seminar by Dr. Woonmi Kim from Institute of Meteorology and Climate Research Karlsruhe Institute of Technology, Germany

11 June 2024
KST 10:00 – 11:00

The Seminar is being held in Room 1010 (Jasmin) – Integrated mechanical engineering building. Click here for the campus map.

Understanding how soil moisture is related to precipitation is important because the relationship between these variables can explain the generation mechanisms of various extreme climate events such as droughts and heatwaves. Both variables are tightly coupled, defining the hydrological cycle on the land. In this presentation, we present findings from two ongoing research projects on the relationship between precipitation and soil moisture, and their effects on extreme climate.

In the first part, we investigate the associations between seasonal precipitation intermittency (PI) and soil moisture across the globe in observation-based datasets (ERA5, MSWEP, and GLEAM) and model simulations (CESM2 Large Ensembles – LENS2) for the period 1981–2020. To quantify the associations between PI and soil moisture, we perform a conditional regression analysis of 10cm soil moisture onto a metric of PI. The results show that PI and SM are generally negatively associated. These associations are explained by increased runoff under higher PI. The effect is much clearer over the regions where the land-atmosphere interactions are positive. Spatial consistency in the associations is found between the observations and CESM2, although noticeable differences exist in the magnitudes of the regression coefficients between these two datasets. We attribute these differences to varying runoff sensitivity between land models.

In the second part, we examine the roles of soil moisture in exacerbating anomalous heatwaves, by performing a case study on the 2023 late-summer heatwave in southeastern South America. Extremely dry soil conditions caused by multi-year La Niña were the primary cause of the heatwave intensification. Dry soil amplified the soil-temperature coupling and increased the daily maximum temperature for 15 days. Attribution analysis performed with an analog-based dynamical adjustment method supports the roles of soil moisture in the heatwave intensity, indicating around 30% of the observed temperature during the heatwave can be attributed to this factor.

Overall, our study emphasizes the importance of soil moisture in driving heatwaves, quantifies statistically the relationships between precipitation intermittency and soil moisture, and highlights observation and model differences in these relationships. These differences can also affect future climate projections for extreme hydrological events.