The Intergovernmental Panel on Climate Change (IPCC) Technical Paper Climate Change and Water draws together and evaluates the information in IPCC Assessment and Special Reports concerning the impacts of climate change on hydrological processes and regimes, and on freshwater resources – their availability, quality, use and management. It takes into account current and projected regional key vulnerabilities, prospects for adaptation, and the relationships between climate change mitigation and water. Its objectives are:

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Climate change and water.

It is now well established that forested catchments have higher evapotranspiration than grassed catchments. Thus land use management and rehabilitation strategies will have an impact on catchment water balance and hence water yield and groundwater recharge. The key controls on evapotranspiration are rainfall interception, net radiation, advection, turbulent transport, leaf area, and plant-available water capacity. The relative importance of these factors depends on climate, soil, and vegetation conditions. Results from over 250 catchments worldwide show that for a given forest cover, there is a good relationship between long-term average evapotranspiration and rainfall. From these observations and on the basis of previous theoretical work a simple two-parameter model was developed that relates mean annual evapotranspiration to rainfall, potential evapotranspiration, and plant-available water capacity. The mean absolute error between modeled and measured evapotranspiration was 42 mm or 6.0%; the least squares line through the origin had as lope of 1.00 and a correlation coefficient of 0.96. The model showed potential for a variety of applications including water yield modeling and recharge estimation. The model is a practical tool that can be readily used for assessing the long-term average effect of vegetation changes on catchment evapotranspiration and is scientifically justifiable.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000WR900325

Response of mean annual evapotranspiration to vegetation changes at catchment scale

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Hydrological functions of tropical forests: not seeing the soil for the trees?

A frequently encountered difficulty in assessing model-predicted land–atmosphere exchanges of moisture and energy is the absence of comprehensive observations to which model predictions can be compared at the spatial and temporal resolutions at which the models operate. Various methods have been used to evaluate the land surface schemes in coupled models, including comparisons of model-predicted evapotranspiration with values derived from atmospheric water balances, comparison of model-predicted energy and radiative fluxes with tower measurements during periods of intensive observations, comparison of model-predicted runoff with observed streamflow, and comparison of model predictions of soil moisture with spatial averages of point observations. While these approaches have provided useful model diagnostic information, the observation-based products used in the comparisons typically are inconsistent with the model variables with which they are compared—for example, observations are for points or a...

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A Long-Term Hydrologically Based Dataset of Land Surface Fluxes and States for the Conterminous United States*

Ecosystem services, the benefits that people obtain from ecosystems, are a powerful lens through which to understand human relationships with the environment and to design environmental policy. The explicit inclusion of beneficiaries makes values intrinsic to ecosystem services; whether or not those values are monetized, the ecosystem services framework provides a way to assess trade-offs among alternative scenarios of resource use and land- and seascape change. We provide an overview of the ecosystem functions responsible for producing terrestrial hydrologic services and use this context to lay out a blueprint for a more general ecosystem service assessment. Other ecosystem services are addressed in our discussion of scale and trade-offs. We review valuation and policy tools useful for ecosystem service protection and provide several examples of land management using these tools. Throughout, we highlight avenues for research to advance the ecosystem services framework as an operational basis for policy d...

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The Nature and Value of Ecosystem Services: An Overview Highlighting Hydrologic Services

Part 1 Introduction: Frank Law and the Stocks Reservoir controversy Frank Law's studies the plynlimon catchment results the Plynlimon forest lysimeter the Thetford micrometeorological and soil physical studies. Part 2 Physics and physiology of evaporation: the Dalton equation the "del" approximation and the combination equation the Penman equation physiological resistance - the Penman-Monteith equation. Part 3 The interception process: the rutter interception model the stochastic interception model. Part 4 Further transpiration studies in the uplands. Part 5 Rainfall interception from short vegetation - the "wet surface" lysimeter experiment. Part 6 Gamma - Ray Attenuation studies of rainfall interception from forests. Part 7 Plastic-sheet net-rainfall gauge measurements of forest interception. Part 8 Evaporation from snow covered vegetation. Part 9 Predicting the effects of land use change - evaporation models. Part 10 Implications of upland afforestation - a case study, Crinan canal.

Ian R. Calder

Papers

Evaporation in the Uplands

Hydrologic effects of land-use change.

The impact of land use change on water resources in sub-Saharan Africa: a modelling study of Lake Malawi

A stochastic model of rainfall interception

An objective assessment of soil-moisture deficit models