Potential of sand dams to increase the adaptive capacity of drylands to climate change

Transcription

1 Potential of sand dams to increase the adaptive capacity of drylands to climate change Presented by: Simon Maddrell, Founder Excellent Development All documents on DropBox at bit.ly/sanddams or USB at back of room

2 Why Drylands? Drylands & Climate Change What are Sand Dams? What is Adaptive Capacity? Measuring Adaptive Capacity using NDVI How Sand Dams enable increased Adaptive Capacity Hydrological Impacts Sustainability Multi-Use Water Source Sustainable Land Management Climate-Smart Agriculture 2 Adaptive Capacity of Sand Dams

3 Why Drylands? Drylands: Home to 2.3 billion people 35% of global population Cover 41% of the Earth s land Make up 44% of the world s cultivated land. Sustain 50% of the world s livestock. Sustain the lives of 74% of the world s poor. Drylands are the battleground for some of the world s most critical global problems: Water & food insecurity, poverty, bio-diversity loss, desertification and climate change

4 Drylands & Climate Change Access to improved water sources is 0-60%. Communities spend up to 12 hours a day just collecting water. Up to 40% of rainwater is lost as run-off. Soil loss reduces adaptive capacity of land. Frequency of droughts to increase Intensity of rains to increase Reductions in annual rainfalls in most areas Rainwater Harvesting & Sustainable Land Mgt. critical interventions to adapt to climate change

5 Sand Dam Animation 2m 38secs 5 What are Sand Dams?

6 Adaptive Capacity: The ability or potential of a system to respond successfully to climate variability & change in order to reduce vulnerability or enhance resilience. (Adger et al., 2007) A proxy measure we can use to understand this is Normalised Difference Vegetation Index (NDVI). In other words how vegetation density changes over time 6 What is Adaptive Capacity?

7 Normalised Difference Vegetation Index (NDVI) NDVI uses visible & near infrared values to establish vegetation density. NDVI is the most commonly used index for vegetation density measured using satellite imagery. 4 sand dam & control sites in a similar-type valley, Makueni County, Kenya during 13 drought instances * 7 * Ryan, C. & Elsner, P. 2007

8 Results: Mean NDVI higher over drought periods Ryan & Elsner, 2016 NDVI at Sand Dam sites is consistently, statistically and substantially higher. Sand Dams maintained NDVI consistently above the threshold for vegetated surfaces. (1.22 vs 0.72 for the control) 8 Impact of Sand Dams

9 Mean NDVI in Drought & Extreme Drought Conditions Condition Sand Dam Control Drought Extreme Drought (0.018) (0.166) Sand Dam Impacts: (Ryan & Elsner, 2016) Drought Conditions: NDVI was 2.5 times greater Extreme Drought Conditions: NDVI was 1.4 times greater 9 Impact of Sand Dams

10 Mean NDVI Results: Light rains conditions Relative greening effect after light rains (recovery after rains) was much greater at sand dam sites Relative Greening NDVI Sand Dams 0.37 Controls Kenya Arid Lands Region Ave.* 0.32 * Drought & non-drought periods (Ryan & Elsner, 2016) Sand Dam Site NDVI typically represented healthy savannah or woodland vegetation. Control Site NDVI typically represented grass and shrubland vegetation. 10 Impact of Sand Dams

11 Net Primary Productivity (NPP) The amount of carbon retained by plants after photosynthesis and respiration. An indicator of amount of carbon that is fixed by plants and therefore potential yield from crops, pasture and wood. NPP Units: Grams of Carbon per m 2 per Year. NPP is a central component of the carbon cycle and can be calculated from NDVI. 11 Measuring Adaptive Capacity

12 Results: Improvements in NPP with Sand Dams NDVI can be correlated to NPP values for different vegetation types * Control Sites Sand Dam Sites NPP Impact Bare soil & sparse vegetation Sand Dams Grassland vegetation +35% With light rain/relative greening impacts increase: Grassland vegetation Sand Dams Savannah & Woodland +47% +123% * NPP Units (calculated from NDVI): Grams of Carbon per m 2 per Year * Source: Prince and Goward (1995); Zheng et al. (2003); Running et al. (2004). 12 Measuring Adaptive Capacity

13 Conclusion (Ryan & Elsner, 2016): Sand dams are an effective approach to increase the adaptive capacity of drylands by increasing the resilience of vegetation through times of water scarcity. The presenter also argues that sand dams reduce the vulnerability of livelihoods & well-being can contribute to increased carbon sequestration can contribute to reducing bio-diversity loss What enables Sand Dams to do this?

14 Hydrological Impacts of Sand Dams References: Hut, Ertsen et al., L. Borst & S.A. de Haas, Rosa Orient Quilis, Sand Dams recharge & raise the water table: The water table rises both upstream & downstream of the sand dam Sand Dam water volumes increase every year (compared to no dam) Sand Dams reach storage maturity (& remain stable) in four years Sand Dams are useful to store water between the wet & dry season Sand Dams also store water between years, building resilience 14 Hydrological Impacts of Sand Dams

15 Sustainability of Sand Dams Sand Dams last over 100 years Virtually zero operation & maintenance costs: 5% need one-off repairs 2% technical failure rate (70% technical failures repaired) Built 1985 Built in Mwala District, Kenya, Drank 2013 MSc dissertation Technical summary Sustainability Cate Ryan

16 Nearly 1 Million People since 2002 Clean Water* for People: All year around within mins of their home 16 Multi-Use Water Source

17 Water for Livestock & Wildlife Multi-Use Water Source

18 Nearly 1 Million Trees since 2002 Irrigation for Vegetable & Tree Nurseries 18 Multi-Use Water Source

19 2 Million days invested in self-help projects since 2002 Saving 2-10 hours per day enables communities to invest in sustainable development of their land. Saved nearly 1 Billion hours collecting water since Sustainable Land Management

20 Virtuous Cycle of Soil & Water Conservation Terraces Retain more water & soil in farms Maintain water & soil in farms Trees Water for people, livestock, vegetables & tree nurseries Sand Dams 20 Sustainable Land Management

21 Terracing land to conserve Soil & Water Over 1.5 Million metres since Sustainable Land Management

22 Climate-smart Agriculture: Agroforestry Drought-tolerant crops Intercropping Cover crops Use of manure 22 Sustainable Agriculture

23 Further reading: The potential of sand dams to increase the adaptive capacity of East African drylands to climate change (Ryan, C. & Elsner, P., Regional Environmental Change, March 2016) All documents on DropBox at bit.ly/sanddams or USB at back of room Available on Excellent USB or Open Access on-line at: