Atmosphere Ocean Science Friday Seminar

Two talks from our new students

Speaker: Tea Susskind and Riddhima Puri, CAOS

Location: Warren Weaver Hall 1314

Date: Friday, September 15, 2023, 4 p.m.


Understanding changes in the South Asian monsoon is critical for agricultural activities and water availability supporting the livelihood of billions. Seasonal monsoon rainfall has been observed to weaken over the late 20th century in the core convergence region of central India. Anthropogenic aerosols and land-use/land-cover changes, both substantial external forcings in South Asia, have been suggested to play a role in driving these changes. In this talk I present my Master’s thesis work on studying long-term historical monsoon changes and their attribution to these two external forcings using a state-of-the-art atmosphere-ocean coupled general circulation model from the Institut Pierre-Simon Laplace Climate Modelling Centre as part of the Coupled Model Intercomparison Project Phase 6 (CMIP6).We find that aerosols are primarily responsible for the long-term seasonal rainfall weakening, though land-use/land-cover changes have also suppressed rainfall over the second half of the 20th century. A subseasonal analysis distinguishing the contributions of the two forcings on historical changes reveals that both have potential positive feedback on the decrease in JulySeptember monsoon precipitation over the late 20th century, modifying radiation balance, energy fluxes, temperature gradients, and circulation. They create unfavorable conditions for monsoon rainfall over the core region by reducing the moist static energy and the southwesterly flow. We further highlight the importance of soil-moisture-feedback processes in the case of land-use/land-cover changes which shows significant warming and drying in the dry and semi-arid northwest part. The study confirms that land cover changes have similar effects as aerosols in driving monsoon weakening.

Up-to-date estimates of changes in groundwater storage are crucial to ensure water security in a warming world. On local scales, the widely used well-based estimates and groundwater flow models are often years out of date due to on-the-ground data requirements. A promising novel approach is to use a combination of remote sensing (satellite/airborne) and ground based data to estimate changes in groundwater storage using the water balance equation. This technique benefits from rapid computation, transferability, and a reduced need for ground based data. The goal of this study was to apply the remote sensing-based water balance technique to estimate changes in groundwater storage in a small (2846 km2) region of the Central Valley of California, and compare the results to independent estimates derived from wells and the groundwater model currently used by water management. Results using remote sensing datasets showed modest agreement in the Butte Subbasin, suggesting that a remote sensing approach can provide useful estimates of groundwater storage on a much shorter timescale than previously attempted.