The ecosystems of the dry tropics are in flux: the savannas, woodlands and dry forests that together cover a greater area of the globe than rainforests are both a source of carbon emissions due to deforestation and forest degradation, and also a sink due to the enhanced growth of trees. However, both of these processes are poorly understood, in terms of their magnitude and causes, and the net carbon balance and its future remain unclear. This gap in knowledge arises because we do not have a systematic network of observations of vegetation change in the dry tropics, and thus have not, until now, been able to use observations of how things are changing to understand the processes involved and to test key theories. Satellite remote sensing, combined with ground measurements, offers the ideal way to overcome these challenges, as it can provide regular, consistent monitoring at relatively low cost. However, most ecosystems in the dry tropics, especially savannas, comprise a mixture of grass and trees, and many optical remote sensing approaches (akin to enhanced versions of the sensors on digital cameras) struggle to distinguish changes between the two. Long wavelength radar remote sensing avoids this problem as it is insensitive to the presence of leaves or grass, and also is not affected by clouds, smoke or the angle of the sun, all of which complicate optical remote sensing. Radar remote sensing is therefore ideal to monitor tree biomass in the dry tropics. We have successfully demonstrated that such data can be used to accurately map woody biomass change for all 5 million sq km of southern Africa. In SECO we will create a network of over 600 field plots to understand how the vegetation of the dry tropics is changing. and complement this with radar remote sensing to quantify how the carbon cycle of the dry tropics has changed over the last 15 years. This will provide the first estimates of key carbon fluxes across all of the dry tropics, including the amount of carbon being released by forest degradation and deforestation and how much carbon is being taken up by the intact vegetation in the region. By understanding where these processes are happening, we will improve our knowledge of the processes involved. W will use these new data to improve the way we model the carbon cycle of the dry tropics, and test key theories. The improved understanding, formalised into a model, will be used to examine how the dry tropics will respond to climate change, land use change and the effects of increasing atmospheric CO2. We will then be able to understand whether the vegetation of the dry tropics will mitigate or exacerbate climate change, and we will learn what we need to do to maintain the structure of the dry tropics and preserve its biodiversity. Overall, SECO will allow us to understand how the vegetation of the dry tropics is changing, and the implications of this for the global carbon cycle, the ecology of savannas and dry forests, and efforts to reduce climate change. The data we create, and the analyses we conduct will be useful to other researchers developing methods to monitor vegetation from satellites, and also to those who model the response of different ecosystems to climate and other changes. Forest managers, ecologists and development practitioners can use the data to understand which parts of the world's savannas and dry forests are changing most, and how these changes might be managed to avoid negative impacts that threaten biodiversity and the livelihoods of the 1 billion, mostly poor, rural people who live in this region.

East Africa (EA) has one of the world's fastest growing populations, with maxima around water-bodies and rapid urbanisation. Climate change is adding to existing problems increasing vulnerability of the poorest. HyCRISTAL is driven by EA priorities. EA communities rely on rainfall for food via agriculture. EA's inland lakes are rain-fed and provide water, power and fisheries. For EA's growing cities, climate impacts on water resources will affect water supply & treatment. HyCRISTAL will therefore operate in both urban & rural contexts. Change in water availability will be critical for climate-change impacts in EA, but projections are highly uncertain for rain, lakes, rivers and groundwater, and for extremes. EA "Long-Rains" are observed to be decreasing; while models tend to predict an increase (the "EA Climate paradox") although predictions are not consistent. This uncertainty provides a fundamental limit on the utility of climate information to inform policy. HyCRISTAL will therefore make best use of current projections to quantify uncertainty in user-relevant quantities and provide ground-breaking research to understand and reduce the uncertainty that currently limits decision making. HyCRISTAL will work with users to deliver world-leading climate research quantifying uncertainty from natural variability, uncertainty from climate forcings including those previously unassessed, and uncertainty in response to these forcings; including uncertainties from key processes such as convection and land-atmopshere coupling that are misrepresented in global models. Research will deliver new understanding of the mechanisms that drive the uncertainty in projections. HyCRISTAL will use this information to understand trends, when climate-change signals will emerge and provide a process-based expert judgement on projections. Working with policy makers, inter-disciplinary research (hydrology, economics, engineering, social science, ecology and decision-making) will quantify risks for rural & urban livelihoods, quantify climate impacts and provide the necessary tools to use climate information for decision making. HyCRISTAL will work with partners to co-produce research for decision-making on a 5-40 year timescale, demonstrated in 2 main pilots for urban water and policies to enable adaptive climate-smart rural livelihoods. These cover two of three "areas of need" from the African Ministerial Council on Environment's Comprehensive Framework of African Climate Change Programmes. HyCRISTAL has already engaged 12 partners from across EA. HyCRISTAL's Advisory Board will provide a mechanism for further growing stakeholder engagement. HyCRISTAL will work with the FCFA global & regional projects and CCKE, sharing methods, tools, user needs, expertise & communication. Uniquely, HyCRISTAL will capitalise on the new LVB-HyNEWS, an African-led consortium, governed by the East African Community, the Lake Victoria Basin Commission and National Meteorological and Hydrological agencies, with the African Ministerial Conference on Meteorology as an observer. HyCRISTAL will build EA capacity directly via collaboration (11 of 25 HyCRISTAL Co-Is are African, with 9 full-time in Africa), including data collection and via targeted workshops and teaching. HyCRISTAL will deliver evidence of impact, with new and deep climate science insights that will far outlast its duration. It will support decisions for climate-resilient infrastructure and livelihoods through application of new understanding in its pilots, with common methodological and infrastructure lessons to promote policy and enable transformational change for impact-at-scale. Using a combination of user-led and science-based management tools, HyCRISTAL will ensure the latest physical science, engineering and social-science yield maximum impacts. HyCRISTAL will deliver outstanding outputs across FCFA's aims; synergies with LVB-HyNEWS will add to these and ensure longevity beyond HyCRISTAL.