Assessing the Implications of Water Harvesting Intensification on - PowerPoint PPT Presentation

Assessing the Implications of Water Harvesting Intensification on Upstream-Downstream Social-Ecological Resilience: A case study in the Lake Tana Basin Yihun Dile a,b , Raghavan Srinivasan c , Louise Karlberg b , and Johan Rockström a a Stockholm Resilience Center, Stockholm University, Stockholm, Sweden b Stockholm Environment Institute, Stockholm, Sweden c Texas 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

Data Area Land cover types (% 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 Area FAO soil name (% 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 4

Model setup and simulation  Basin Area: 15129 km 2  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  Hargreaves’s method  Surface runoff estimation  Curve number method  Stream routing  Variable storage method  Hydrological data  1990-2007

Management  Two reserviors Principal spillway Emergency spillway Elevation * Area(km 2 ) Volume(Mm 3 ) Elevation Area(km 2 ) Volume(Mm 3 ) Lake Tana 1784 2,766 20,300 1787 2983 29,100 Angereb 2135 0.5 3.53 2138 0.6 5.16 Reservior  Fertilizer application  Tillage operations  depth of till of 15cm, and  mixing efficiency of 0.3  tillage frequency of 4  Pescticide application  2.4.D amine weed killer  1 liter/ha ~ 0.379kg/ha 6

Model Calibration and Validation at Megech NSE=0.76 NSE=0.74 PBIAS=4.0% PBIAS=40.2%

Model setup and simulations  Subbasins No.: 482  HRUs No.: 786  Total area: 10 sq.km  Subbasin size: 1-6ha  Climate data  rainfall, Max & Min - 1990-2011  Evapotranspiration  Hargreaves’s method  Global weather data – weather genrator  Surface runoff estimation  Curve number method  Stream routing  Variable storage method

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  Tillage operations  depth of till of 15cm, and  mixing efficiency of 0.3  tillage frequency of 4  Pescticide application  2.4.D amine weed killer  1 liter/ha ~ 0.379kg/ha

Water Harvesting Implementation Scenarios Fir irst st cla lass ss su suit itabi ability lity – HRUs that consist of a slope<2%, Soil: Luvisols, and Vertisols; and agricultural land. Area = 0.14km 2 (1.14% of watershed) Second econd clas lass s su suit itabil ability ity – HRUs of slope: <8%; Soil: Luvisols, and vertisols; and agricultural land. Area = 3.79km 2 (38% of watershed) Thi hird cla lass ss su suit itabil ability ity – HRUs of slope: <12%; soil: Luvisols, and vertisols; and agricultural land. Area = 5.07km 2 (51% of watershed) Nut utrient ient sc scenari enarios os  Cu Curr rrent ent nutrie rient nt ap applica cation ion ra rate  TEFF – 1st stage: UREA - 15kg/ha and DAP – 15kg/ha 2nd stage: UREA – 15kg/ha  Onion – 1st stage: UREA – 85kg/ha, and DAP – 30kg/ha 2nd stage: UREA – 85kg/ha  Blanket et Nutrient ient Reco commendat endation ion (B (BNR1) )  TEFF – 1stage: UREA – 50kg/ha, and DAP – 30kg/ha 2nd stage: UREA – 50kg/ha  Onion – 1st stage: UREA – 85kg/ha, and DAP – 30kg/ha 2nd stage: UREA – 85kg/ha  Blanket et Nutrient ient Reco commendat endation ion (B (BNR2) )  TEFF – 1st stage: UREA – 85kg/ha, and DAP – 30kg/ha 2nd stage: UREA – 85kg/ha  Onion – 1st stage: UREA – 85kg/ha, and DAP – 30kg/ha 2nd stage: UREA – 85kg/ha

Change 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

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