A climate change scenario is defined with respect to a climatological baseline, which determines a reference point for the projected climate changes. Climate scenarios that are developed for impacts applications usually require that some estimate of climate change be combined with baseline observational climate data. Thus, the demand for more complete and sophisticated observational data sets of climate has grown in recent years. The important considerations for the baseline include the time period adopted as well as the spatial and temporal resolution of the baseline data. IPCC have usually taken the year '1990' as the baseline year for the presentation of emissions scenarios and for calculations of future climate and sea-level change. '1990' has also been adopted by the United Nations Framework Convention on Climate Change (UNFCCC) in their definition of emissions reductions targets. Choosing a single year as a baseline is appropriate for some applications, but not for climate change studies. Due to climate variability a single year may be unusually warm, cold, dry or wet and thus will not make a useful reference point for measuring climate change. It is more common to use the average climate over a 30-year period to define the baseline climate. A 30-year climatic average smoothes out many of the year-to-year variations in the climate. In addition, the individual 30 years of such a period captures much of the interannual and short time-scale variability of climate that may be relevant for an impact application. The IPCC Data Distribution Centre (IPCC DDC) suggests the period 1961-90 to be used as the baseline period. This period has generally good observed data and it represents the recent climate to which many present-day human or natural systems are likely to be reasonably well adapted. The period also ends in 1990, the year adopted by many IPCC and UN FCCC applications.
Published in Chapter:
Climate Change Impact on the Water Resources of the Limpopo Basin: Simulations of a Coupled GCM and Hybrid Atmospheric-Terrestrial Water Balance (HATWAB) Model
Berhanu F. Alemaw (University of Botswana, Botswana) and Thebeyame Ronald Chaoka (University of Botswana, Botswana)
Copyright: © 2018
|Pages: 24
DOI: 10.4018/978-1-5225-3440-2.ch012
Abstract
This chapter aims to evaluate the impacts of climate change on both hydrologic regimes and water resources of the Limpopo River Basin in southern Africa. Water resources availability in the basin, in terms of, seasonal and annual runoff (R), soil moisture (S) and actual evapotranspiration (Ea) is simulated and evaluated using the hydrological model, HATWAB. These water balances were computed from precipitation (P), potential evapotranspiration (Ep) and other variables that govern the soil-water-vegetation-atmospheric processes at 9.2km latitude/ longitude gird cells covering the basin. The 1961-90 simulated mean annual runoff reveals mixed patterns of high and low runoff across the region. Although relatively small changes in runoff simulations are prevalent among the three climate change scenarios, generally the OSU simulated relatively high runoff compared to the UKTR and HADCM2 GCMs.