GEOGRAPHIC AND SEASONAL DISTRIBUTION OF WATER AVAILABILITY IN THE SESAN CENTRAL HIGHLANDSTarek Ketelsen, Mai Ky Vinh, Jorma Koponen

MK2: Valuing Multiple uses of reservoir waters: WorldFish – ICEM –IFPRI – CIEM – DLOF - CEPA

Sesan Vietnam: land use2005-2009• forested areas rapidly converted

into agricultural land with the expansion of industrial crops– cassava, rubber and coffee

• cashew, rubber, cassava and black pepper are the fastest growing crops (growth of 8-12% p.a.)

• Irrigated rice growing at 3.9%p.a.• Rainfed rice & maize shrinking at

5-7% p.a.

Sesan Vietnam: catchment characteristics

• 3S catchments are highly productive catchments

• 10% of the total Mekong Basin area but contribute 20.5% of the total flow

• Strong monsoon climate => water availability is a question of timing rather than quantity

• Sesan catcment:18,684km2• Sesan Mean annual outflow:

651m3/s (20.5 billion m3/yr)

Purpose of the water balanceAssess:• Surface water resource availability in the

Sesan Vietnam• Contribution of reservoirs (Yali) to surface

water availability• Identify which areas of agricultural land could

benefit from reservoir irrigation

Modelling methodology• VMod model (Koponen et al, 2010)• area-based distribution of hydro-

meteorological impacts of climate change• Computes water balance for grid cells

(5x5km)• Baseline:1981 – 2005• Can predict changes in:

– Rainfall– Runoff– Flows– Infiltration– evapotranspiration

water balance components

Precipitation

Transpiration

Evaporation

Surface run-off

Infiltration

Surface layer water availability

Subsurface layer water availability

Groundwater availability

• Moisture budget– Surface water

availability– Relationship between

precipitation and PET

• Soil water availability– Moisture stored in

the surface and subsurface layers

Sesan Vietnam: Rainfall

Sesan Vietnam: moisture budgetsprecip. - PET

Sesan Vietnam: Water availability

Sesan Vietnam: Soil moisture availability

Sesan Vietnam: “Agricultural drought”Precipitation < 0.5* PET

• Districts surrounding Sesan hydropower are ‘hotspots’ for agricultural drought during the dry and transition seasons– Sathay– Ia Grai– Kon Tum– Chu Pah

• Agricultural land in these areas could benefit from reservoir irrigation to:– Expand agriculture into new areas– Reduce rising demand for

groundwater irrigation in the Sesan

Catchment water availability• Northern mountainous districts

in Kon Tum are wettest (e.g. Dak Glei)

• Southern districts in Gia Lai are driest (e.g. Chu Se)

• Central districts of Sesan Vietnam are more prone to water stress or extreme dry periods

Reservoir contribution to water availability• Reservoirs regulate the

seasonal availability of water increasing productivity for electricity generation

• Can they also improve agricultural productivity?

• Which contribution is more valuable?

Yali Buffer zone• Within 2km of the

reservoir• Sa Thay, Kon Tum

and Chu Pah districts

Yali buffer zone

Yali: inflow hydrology• Contributing catchment:

3,878km2• Mean annual flow:

262m3/s (40-950m3/s)• Annual inflow volume:

47,327 – 175,434 m3 (average: 98,724m3)

Yali reservoir storage• Drawdown :25m (515-490masl)• Drawdown area: 30.2km2• FSL Vol: 981.5mcm• LSL Vol: 215.5mcm• Live storage: 766mcm• Evaporation losses: ~50mcm/yr• => ~700mcm of ”productive water”

Source: (Räsänen et al, 2012

Reservoir water productivity

• ~700 mcm of productive water• => 3,600-3,800GWh• => USD ?• How much water could be used in surrounding agricultural

land?• How productive would this water be compared to hydro-

electric generation?

Source: (Räsänen et al, 2012

Thank you!