Can we measure evapotranspiration from space? And when a satellite produces a map of crop water use, how certain are those numbers?

Dr. Gilles Boulet joins host Veena Srinivasan for a deep dive into one of the most important and difficult-to-measure components of the hydrological cycle: evapotranspiration.

Evapotranspiration, or ET, combines evaporation from soil with transpiration through vegetation. In many semi-arid landscapes, it accounts for most of the water leaving the land surface. However, measuring ET across individual farms, irrigation commands, and entire watersheds is remarkably difficult.

In this episode, Gilles and Veena unpack what satellites actually observe, from vegetation and radar signals to land-surface temperature. They also discuss how scientists turn those observations into estimates of evapotranspiration.

They explore the role of flux towers and scintillometers, why satellite ET products contain uncertainty, and the differences between contextual and physics-based modeling approaches.

The conversation also looks ahead to TRISHNA, the Indo-French thermal-infrared satellite mission that aims to provide much more frequent land-surface-temperature observations at field-relevant spatial scales.

Additionally, the conversation answers questions regarding how better ET observations could help irrigation departments and groundwater agencies understand where water is actually being consumed, and whether we are close to producing reliable, near-daily maps of agricultural water use.

Dr. Gilles Boulet is a senior scientist at IRD and works with the Indo-French Cell for Water Science at the Indian Institute of Science, Bengaluru. His research focuses on land-surface processes, remote sensing, evapotranspiration, and field instrumentation.

The Water Data Podcast is a talk show on the science, systems, and stories of water, hosted by Veena Srinivasan.

For all references and further readings related to the episode, visit https://welllabs.org/wdp-gilles-boulet/

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Recording by Nabina Chakraborty, Vraj Acharya and Nanditha Gogate. Video editing by Srisabari Varaguna Pandian. Graphics and artwork by Aparna Nambiar and Kanishka Goyal. Audio mixing and mastering by Vijay Doiphode. Podcast production and management by Nabina Chakraborty and Pavan Srinath.