Land impacts on mesoscale convective systems

The challenge

An understanding of how intense storms known as Mesoscale Convective Systems (MCS) will change as the world warms is urgently needed in order to build climate-resilient homes, roads, bridges and dams in hotspot regions.

This project will significantly advance understanding of how the land surface affects MCSs across the world, and thus inform estimations of extreme convective rainfall in future decades.

Background

Mesoscale Convective Systems (MCSs) are among the most powerful storms in the world and in many places are the dominant cause of hazards such as high winds, lightning, flash flooding and tornadoes. They are particularly prevalent in certain “hotspot” regions including Northern Argentina and India, West and Central Africa, and the US Great Plains, where a combination of warm, moist air and favourable winds support their development.

MCSs result from thunderstorms that organize into a single large complex measuring hundreds of kilometres wide and which travel across the land for hours or, in some cases, days, causing extraordinary downpours along their path. These long-lived, damaging storms are responsible for nearly 80% of extreme rain over tropical land and are particularly sensitive to climate change, yet are poorly represented by conventional climate models.

An understanding of how MCSs will change as the world warms will help to build climate-resilient homes and infrastructure such as roads, bridges and dams in hotspot regions.

Mesoscale convective systems - in numbers

100km

MCS result from storms that can organise into a single complex measuring 100s of kilometres

>10cm

Amount of rainfall that can fall in one hour, with often extraordinary downpours

33%

Increase in intense West African storms in just 35 years

Summary

Conventional climate models lack sufficient spatial resolution to realistically simulate Mesoscale Convective Systems. New “Convection Permitting Models” (CPMs) however can represent MCSs and are starting to deliver improved predictions and better understanding of how MCSs respond to their environment.

We know that spatial patterns in vegetation and soil humidity affect air temperature, moisture and wind flows, and that these changes can affect where (or indeed whether) a powerful MCS develops. We are already seeing rapid MCS intensification in West Africa due to an increasing temperature gradient between desert and forest regions. Moreover at smaller scales, soil moisture strongly controls West African MCS life-cycles.

This project will focus on how MCSs are affected by patterns of soil moisture and vegetation, through analysis of both satellite observations and CPMs. The work will discover how strong land effects are across the different hotspots of the world, and what processes are key to determining that strength.

Results will benefit weather prediction, climate change prediction, model evaluation and development and research on land-rainfall feedbacks and organised convection.

Early warning, early action

The research will provide the knowledge to improve the prediction of storm hazards and inform decision-making across weather to climate change time-scales.