SAT-EX: The global ecosystem more limited in water than expected

#STEREO, #Climate change, #Water, #Drought, #Webstory

Published on 23 March 2020

This March 23rd, the World Meteorological Organization commemorates its 70 years of existence. The theme chosen for this important anniversary is aligned with that of World Water Day 2020, celebrated yesterday, namely "Climate & Water".

More extreme events

Climate change has a major effect on water. The rise in temperatures notably increases the evaporation rate, which accelerates the hydrological cycle. This can lead to increased precipitation in some regions and more severe droughts in others, depending on the movement of traditional rain belts.

In many parts of the world, the seasonal precipitation patterns are becoming more irregular, affecting agriculture and food security as well as the livelihoods of millions of people who work the land.

Climate models predict worsening extreme events, such as droughts, intense precipitation and heat waves. But the projections of the various current models do not always overlap. The improvement of these models is essential in order to be able to provide decision-makers with reliable tools to better manage water resources but also to determine the global terrestrial carbon budgets.

The STEREO project SAT-EX has produced significant results in this context, results which can be directly used by the entire scientific community interested in climate and in particular by experts specialized in climate modeling.

I call on all stakeholders to step up climate action and invest in robust adaptation measures to ensure the sustainability of water. By limiting global warming to 1.5 ° C, the world will be in a much better position to manage and overcome the water crisis that we all face.

António Guterres, Secretary-General of the United Nations

Search the past to predict the future

The main objective of the SAT-EX project was to study and quantify the climate factors that limit the growth of the world's vegetation in order to predict the impact of climate change on ecosystems. The team studied an impressive amount of satellite data, including no less than 30 years of consistent global records of crucial environmental and climatic variables.

This painstaking endeavour allowed them to unravel the processes behind climate extremes, to discover the spatiotemporal scales at which they operate and to understand their impact on terrestrial biomass. Archive data is also an observational reference for assessing the ability of climate models to represent climatic extremes and vegetation dynamics.

Water, the first limiting factor

The main climate factors affecting vegetation are water availability, solar and atmospheric radiation and air temperature. The SAT-EX researchers were able to demonstrate that the availability of water is the most important factor for plant growth for almost two thirds of the continental vegetation.

Most tropical and high latitude regions are limited primarily by radiation or temperature.

This importance of water availability for most of the world is clearly more striking than what was previously reported and is reinforced by the long memory of soil moisture. Precipitation can indeed affect the vegetation dynamics occurring more than three months later, especially in semi-arid regions.

The results also highlight the very complex relationships between climate and vegetation dynamics. The dependence of the world's vegetation on water availability suggests that, over a large part of the continents, vegetation could imitate the changes in water availability expected as a result of climate change. The consequences could be significant for mid-latitude ecosystems which should receive less precipitation in the decades to come.