Assessing the Implications of Water Harvesting ... ? Assessing the Implications of Water Harvesting

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Assessing the Implications of Water Harvesting Intensification on Upstream-Downstream Social-Ecological Resilience: A case study in the Lake Tana Basin Yihun Dilea,b, Raghavan Srinivasanc, Louise Karlbergb, and Johan Rockstrma aStockholm Resilience Center, Stockholm University, Stockholm, Sweden bStockholm Environment Institute, Stockholm, Sweden cTexas A&M University, Texas, USA Rationales Rainfall variability dryspells and droughts Dry spells Drought Water harvesting systems can bridge this rainfall variability In-situ water harvesting Ex-situ water hatvesting ? Upstream-downstream implications Research Area WH suitability study Hydrological Modelling Understanding implications 4 Data Land cover types Area (% of basin) Dominantly cultivated 51.35 C2: Moderatly cultivated 22.34 Woodland open; Shrubland; Afro alpine; Forest 2.91 Grassland 2.83 Water body 20.19 FAO soil name Area (% of basin) Texture Eutric Leptosols 12.38 LOAM Haplic Nitisols 1.29 CLAY_LOAM Chromic Luvisols 16.00 CLAY_LOAM Eutric Vertisols 11.74 CLAY Eutric Cambisols 0.01 LOAM Eutric Fluvisols 9.79 LOAM Haplic Luvisols 20.62 LOAM Eutric Regosols 0.28 SANDY_LOAM Lithic Leptosols 2.86 CLAY_LOAM Haplic Alisols 4.77 CLAY Basin Area: 15129 km2 Total No subbasins: 959 Subasin sizes: 500-3000ha Total No HRUs: 9963 Flow calibrated at 3 gauging stations Climate data rainfall, Max & Min - 1990-2011 Global weather data weather genrator Evapotranspiration Hargreavess method Surface runoff estimation Curve number method Stream routing Variable storage method Hydrological data 1990-2007 Model setup and simulation 6 Management Two reserviors Principal spillway Emergency spillway Elevation* Area(km2) Volume(Mm3) Elevation Area(km2) Volume(Mm3) Lake Tana 1784 2,766 20,300 1787 2983 29,100 Angereb Reservior 2135 0.5 3.53 2138 0.6 5.16 Tillage operations depth of till of 15cm, and mixing efficiency of 0.3 tillage frequency of 4 Fertilizer application Pescticide application 2.4.D amine weed killer 1 liter/ha ~ 0.379kg/ha Model Calibration and Validation at Megech NSE=0.76 PBIAS=4.0% NSE=0.74 PBIAS=40.2% Subbasins No.: 482 HRUs No.: 786 Total area: 10 sq.km Subbasin size: 1-6ha Climate data rainfall, Max & Min - 1990-2011 Evapotranspiration Hargreavess method Global weather data weather genrator Surface runoff estimation Curve number method Stream routing Variable storage method Model setup and simulations Management Ponds implemented as reserviors size that can store water for ONSEASON and OFFSEASON irrigation size determined for combination of different climatic years & nutrient application Crop rotation is applied ONSEASON (July-Dec) TEFF OFFSEASON (Jan-April) Onion Fertilizer Current fertilizer application for TEFF Blankert fertilizer recommendation (MoAR) for TEFF Blanker fertilizer recommendation for Onion Pescticide application 2.4.D amine weed killer 1 liter/ha ~ 0.379kg/ha Tillage operations depth of till of 15cm, and mixing efficiency of 0.3 tillage frequency of 4 Water Harvesting Implementation Scenarios First class suitability HRUs that consist of a slopeChange in crop yield (%) Change in crop yield (%) Change in biomass (%) Change in biomass (%) Onion production (ton/ha) year IRR VOL(m^3) WYLD(m^3) percentage 1995 (drier) 532,485.68 1,839,334.07 28.95 2000 (wetter) 309,326.90 7,063,383.30 4.38 Discussion and conclusion U/S Benefits/costs D/S Benefits/costs Crop yield +++ + Biomass +++ + Soil loss ++ ++ Low flows + ++ Peak flows + ++ Total flow - Win-Win Thank you

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