The challenge of HIV/AIDS: Where does agroforestry fit in? - World ...
The challenge of HIV/AIDS: Where does agroforestry fit in? - World ...
The challenge of HIV/AIDS: Where does agroforestry fit in? - World ...
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Chapter 12: Watershed functions <strong>in</strong> productive agricultural landscapes105Way BesaiMae ChaemDaily ra<strong>in</strong>fall (station level) mm day 1DaysADaily ra<strong>in</strong>fall (station level) mm day 1DaysBCDRiver flow m 3 sec –1River flow mm 3 sec –1DaysDaysFigure 2. <strong>The</strong> records <strong>of</strong> ra<strong>in</strong>fall (A and B) and river discharge (C and D) <strong>of</strong> the Way Besai for the 1975–1998 period (A and C), and MaeChaem for the 1988–2000 period (B and D). <strong>The</strong> th<strong>in</strong> dark l<strong>in</strong>es trace the maxima and m<strong>in</strong>ima <strong>of</strong> daily values for the observation periods,the solid lighter l<strong>in</strong>e <strong>in</strong>dicates the mean daily values (van Noordwijk et al. 2003).the other <strong>in</strong>dicators the trade-<strong>of</strong>f expla<strong>in</strong>edonly a small part <strong>of</strong> the total variation. Thissuggests that <strong>in</strong> this catchment area the potentialdownstream bene<strong>fit</strong>s <strong>of</strong> more waterare not associated with negative changes <strong>in</strong>river flow dur<strong>in</strong>g the driest month or withless buffer<strong>in</strong>g <strong>of</strong> peak events.A spatially distributed water balance modeldeterm<strong>in</strong>ed the current land cover situationas be<strong>in</strong>g between natural vegetation <strong>of</strong>forest on a porous soil, and degraded landwith grassland on a compacted soil. Withoutf<strong>in</strong>e-tun<strong>in</strong>g <strong>of</strong> the model, an acceptableagreement between the model and actualmeasurements was obta<strong>in</strong>ed for the WayBesai (Table 1) and Mae Chaem (Table 2)catchment areas for each <strong>of</strong> the various<strong>in</strong>dicators, with<strong>in</strong> the range <strong>of</strong> forest to degradedlands.This analysis, presented <strong>in</strong> very condensedform here, suggests that changes <strong>in</strong> forestcover can modify a number <strong>of</strong> quantitativecharacteristics <strong>of</strong> river flow, but that ra<strong>in</strong>fall(and any change <strong>in</strong> ra<strong>in</strong>fall characteristicsbetween measurement periods) dom<strong>in</strong>atesthe outflows. As ra<strong>in</strong>fall tends to have complexpatterns <strong>of</strong> variation over time, it is noteasy to tease out a land-use change signalfrom the noisy background. Much <strong>of</strong> theattribution <strong>of</strong> change <strong>in</strong> river flow to landcoverchange <strong>in</strong> public debate may notsurvive close scrut<strong>in</strong>y.By compar<strong>in</strong>g the results from the modelwith the measurements taken <strong>in</strong> the fieldwe can conclude that models that l<strong>in</strong>k thespace–time characteristics <strong>of</strong> ra<strong>in</strong>fall via