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 Rockströma

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

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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 Hargreaves’s method

Surface runoff estimation Curve number method

Stream routing Variable storage method

Hydrological data 1990-2007

Model setup and simulation

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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 Hargreaves’s 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 slope<2%, Soil: Luvisols, and Vertisols; and agricultural land. Area = 0.14km2 (1.14% of watershed) Second class suitability – HRUs of slope: <8%; Soil: Luvisols, and vertisols; and agricultural land. Area = 3.79km2 (38% of watershed) Third class suitability – HRUs of slope: <12%; soil: Luvisols, and vertisols; and agricultural land. Area = 5.07km2 (51% of watershed) Nutrient scenarios Current nutrient application 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 Nutrient Recommendation (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 Nutrient Recommendation (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

Thank you