GroFutures: Groundwater Futures in Sub-Saharan Africa. UpGro Consortium grant 2015-19

Understanding climate impacts on Groundwater

Martin Todd, University of Sussex

m.todd@sussex.ac.uk

Context: Africa is changing rapidly and demand for fresh water will increase

e.g. Demand for piped water in rapidly growing urban centres

• e.g. Intensified agriculture.

Allen and Ingram (2002) Nature

% change in water vapour with warming

% change in global mean precipitation with warming

Global average precipitation ~3% increase per degree C warming

Heavy rainfall may follow C-C relation 7% per degree warming

How might the global water cycle respond to a warmer climate?

Pattern reflects ‘wet get wetter’ vs ‘warmest get wetter’ and other changes to atmospheric circulation(Stippled dots show where change is bigger than internal variability, hatching where change is less than internal variability)

Spatial pattern of change in precipitation is highly variable and uncertain

Climate impacts on groundwater: a neglected issue?

• Groundwater – climate change impact studies lag behind those for surface hydrology– ‘Both detection of changes in groundwater systems and

attribution of those changes to climatic changes are rare owing to a lack of appropriate observation wells and a small number of studies’

– ‘the relation between groundwater and climate change was rarely investigated before 2007’• (IPCC AR5 WG2, 2014)

Initial case studySemi-arid Tanzania(In weathered crystalline rock environments that underlie 40% of sub-Saharan Africa

• Long term data: many decades

• Cover the primary hydrogeological and developmental contexts

Improving our understanding: GroFutures will establish a Network of African Groundwater Observatories

Case study: Episodic recharge at Makutapora in semi-arid Tanzania

Makutapora wellfield supplies capital city

Dodoma

Taylor et al. (2013) Nature Climate Change 3: 374-378.

Provides the longest, published record of groundwater levels anywhere in the tropics

Highly non-linear rainfall-recharge relationshipRecharge occurs only 1 year in 5

Episodic groundwater recharge events linked to global pattern of climate variability

Sub-continent wide pattern of rainfall anomalies associated with the 7 largest GW recharge events

Taylor et al. (2013) Nature Climate Change 3: 374-378.

Timeseries of this rainfall pattern related to ENSO and Indian Ocean Dipole pattern

• Projected increase in seasonal extreme rainfall is greater than for the mean

• This may favour GW recharge

Spread of projected percentage change in mean (left) and 90th percentile rainfall (right) in IPCC AR5 models

Recharge futures?

Taylor et al. (2013) Nature Climate Change 3: 374-378.

Central Tanzania, 2070-99

e.g. WaterGAP: Portmann et al. (2013) Environ. Res. Lett. 8: 024023.

• Large-scale models project a very mixed and uncertain picture

Projected climate change impacts on recharge

Confronting the model world with the real world

Good simulation occurs ‘by chance’ as JULES does not have explicit groundwater recharge process

Makutapora observations

WaterGap model

Jules model

Is this non-linear relationship observed at a few locations in the tropical Africa widespread?

Observations in Africa reveal recharge pathways (focused, non-matrix) completely divorced from models commonly used to estimate recharge

Summary of GroFutures activities

• Data: NAGO network of study sites. High quality, long-term data

• Process understanding: Rainfall-recharge realtionships and recharge pathways

• Models: Improve GW models at study sites

• Future Projections of GW resource: Based on climate and socio-economic developmental scenarios

• GW management and decision-making: Apply ‘pathways’ approach to inform sustainable and ‘pro-poor’ GW development.

GroFutures Pathways Approach

• Pathways analysis rooted in extensive, multi-level stakeholder engagement and multi-criteria mapping

• ‘Open up’ range of GW development pathways: bush paths/motorways

• Evaluate viability and sustainability of identified pathways

Conclusions

• Rapid development in Africa will inevitably result in substantial increases in demand for freshwater

• Sustainable development requires improved understanding of the resource– Initial analysis indicates the need for long term data

across Africa– Model development

• Pro-poor GW management

• GroFutures hopes to address these issues