International Congress on Water 2011 Integrated Water Resources Management in Tropical and Subtropical Drylands

Mekelle, Ethiopia, 19-26 September 2011

Impact of abstractions upstream on the benefits of riverine water discharge

into the Lorian swamps, Kenya

Jan de Leeuw, Shem Kifugo, Zipporah Msiyuni,

Mohamed Said and Don Peden

The problem

• Many African highland rivers discharge in drylands(naturally closed basins)

• Discharge important to downstream users • Secure surface water and forage during dry periods• Recharge of aquifers and wetlands• Opportunities for development

• Retention of agricultural water upstream deprives downstream communities from rivers’ benefits

The Ewaso Ng’iro catchment

Lorian Swamp

To Nairobi

Archer’s Post

Mt. Kenya

Upstream agriculture

Merti

Purpose of the study

• Assess water users’ downstream vulnerability to upstream abstractions Magnitude of upstream abstractionsUpstream and downstream linkages Describe downstream water uses

Permitted abstractions

• Since 2000 2.4 m3.s-1

• Increasing over time • Underestimate

Illegal abstractions Higher in dry periods

Percent of the Total Annual Discharge at Archer's Post

1960 1985 2010

Demand for water

• Estimated demand for water 2000 (Mutiga et al. 2010)

200 million m3.year-1 or 3.6 m3.s-1

≈ 10-15% of annual discharge at Archer’s Post 50% higher than permitted Sesaonally variable

• Low during rainy season • Escalate in dry season when river discharge is low

0.1

1

10

100

1000

1960 1970 1980 1990 2000 2010

Mo

nth

ly d

isch

arge

(m3

.s-1

)

Year

River discharge Archer’s Post

Highly variableLow discharge events more frequent since 1980’s

Number of days per year when discharge does not reach the Lorian Swamp

1950 Year 2010

Impact on Merti aquifer

• Sustains more than 500,000 people

• Aquifer recharges during peak water flow

• Current abstractions appear to have little impact on aquifer

Recharge (km3/year)

Monthly NDVI maps 1998 - 2010

January Month December

2010

Yea

r

199

8

Impact on vegetation biomass

• NDVI fluctuates over time

• Swamp has higher NDVI than surrounding area

Impact on vegetation biomass

• Significant relation water inflow and difference NDVI swamp and surroundings

• Outliers reflect local rains Lorian Swamp

NDVI

Ewaso Ng’iro discharge and ecosystem services Lorian swamp

Water Ecosystem service Benefits

Surface-green

Livestock production Multiple uses

Wildlife conservation Tourism & public good

Domestic use Nutrition and hygiene

Livestock production Multiple uses

Wildlife conservation Tourism & public goods

Surface-blue

Fish production Food & cash

Irrigated crops Food & cash

Ground-blue

Domestic use Nutrition and hygiene

Livestock production Multiple uses 1

Vulnerability to abstractions of the benefits from river water

• Blue surface water – highly vulnerable

• Green water – highly vulnerable

• Groundwater recharge – low vulnerability

Conclusions Abstractions upstream significant, particularly in

dry season

Significant impact water security downstream

Benefits from surface water (green and blue) vulnerable to abstractions

Benefits from groundwater less vulnerable to abstractions

Basin level water productivity depends on upstream-downsream linkages

Recommendations

Stimulate information exchange and dialogue between up and downstream water users

Quantify demands for water in down- and upstream areas with emphasis on dry periods

Consider mechanisms to secure access to water at both ends of basin

After thought Similar eco-hydrological processes underpinning

upstream-downstream linkages:

Naturally closed basins

Closing basins

Rahabiltated streams and springs caused by upslope restoration of land productivity.

Potential for shared learning for management

Thank you!