Nutrient Transport Modelling in the Daugava River Basin - DiVA Portal

moisture.Figure B1. Selection of curve number as a function of antecedentRecommended values of the break points AM1 and AM2 have been used (Dai et al,2000). The 5­day antecedent precipitation is computed as follows:At=t∑ − 1n=t −5( Rn+ Mn)(B4)CN2 k values for different land uses are given in the BasinSim 1.0 User’s Guide (Dai etal, 2000).Values of CN1 k and CN3 k are computed from CN2 k :CN1kCN 2= k(B5)2.334 − 0,01334 ⋅ CN 2kCN3kCN 2= k(B6)0.4036 − 0.0059 ⋅ CN 2kAppendix C. Determination of potentialevapotranspirationPotential evapotranspiration is given by the following equation (Dai et al., 2001):PEt0.021⋅Ht⋅ et=T + 273t(C1)whereH t = number of daylight hours per day during the month containing day te t = saturated water vapour pressure on day t [mbar]T t = daily mean air temperature, average value for entire basin [°C]The saturated water vapour pressure is estimated from daily mean air temperature:32