Extended Abstract

The simulations were performed with the non-hydrostatic limited-area climate model COSMO-CLM(Steppeler et al. 2003; Dobler and Ahrens, 2008). As model input, the initial and lateral boundaryconditions were taken from the ERA-Interim reanalysis. In the present study, the horizontal resolutionwas set to 0.25° with 32 vertical layers. The simulation domain encompassed the entire Indian region(Fig. 1). More details about the model are given at the community website (www.clm-community.eu).In order to assess the influence of soil moisture, we have performed several simulations: areference simulation (CTL) for the period 1989-2008 and perturbed simulations. These lattersimulations are initialized each year at 2 nd April with CTL, but with perturbed soil moisture. For eachyear there are DRY runs with an initialized soil 50% drier and WET runs 50% wetter relative to CTL(with perturbations limited by plant wilting point and field capacity). This setup is motivated by Schäret al. (1999) and Pielke Sr. et al. (1999).3 TheoryHere the S-P feedback/recycling analysis were based by Schär et al (1999), in which they formulatedtwo bulk characteristics: the recycling ratio ß and the precipitation efficiency χ . The recycling modelmakes four basic assumptions: (1) atmospheric flow across the region is approximately unidirectional;(2) water vapor transported across the boundary or evapotranspirated within the region is well mixed;(3) vertical fluxes precipitation P and evapotranspiration ET have minimal spatial variability; and (4) atlong time scales within the investigation period, the changes in atmospheric moisture storage over theregion are neglectable.With the flux integral approach, we can calculate the incoming (IN) and outgoing (OUT) fluxacross any arbitrary boundary line. Also, the three-dimensional problem can be reduced to a twodimensionalproblem through vertical integration of the vapor flux. The recycling ratio is given by ß =ET/(ET+IN) and the precipitation efficiency can be defined as χ = P/(ET+IN).The precipitation changes in the sensitivity experiment (WET and DRY) are estimated by thefollowing equation (see Schär et al 1999):( ∆ET + ∆IN ) + ∆χ( ET + IN )∆P = χ' (1)Where χ ' is the efficiency in the perturbed simulation and the ∆ -terms indicate differences betweenthe perturbed and the control simulations. The first term on the right hand side of the eq. (1) reflects theprecipitation change through direct (recycling) processes and the second term depicts the indirect(feedback) contribution. The results for the different analysis domains (Fig. 1) were made comparableby normalization following Zangvil et al. (2010).4 ResultsFigure 2 depicts inter-annual variation of the recycling ratio β and precipitation efficiency χ of CTLand the soil moisture sensitivity simulations for the analysis domain E and W. The precipitationrecycling ratios are generally in the range of 0.1 to 0.25 with larger values for the northern region (N,the Himalayan region with high precipitation values, but relatively small influx). The recycling strengthincreases with larger evapotranspiration and precipitation, and smaller moisture influx.The bulk characteristics χ is of moderate sensitivity to soil moisture initialization (Fig. 2) inmost of the years with small positive feedback (except for in region W, see Tab. 1). However, someyears (1992 in E, 1993 in W, 1995 in N) experience a negative feedback to soil moisture initializationperturbation. This result is opposite to the results in Schär et al. (1999), where χ always increased-69-