DCOM Volume I Appendix A
1 Appendix A: Climate Change and Resilience to Climate Change
Climate change is now recognized as one of the defining challenges for the 21st century. More frequent and intense extreme weather events have resulted in a higher incidence of floods and droughts around the planet. The ensuing adverse impacts of climate change on water and sanitation services constitute a clear and present danger for development and health. Ensuring optimal resilience of water and sanitation services in a globally changing climate context will be crucial for maintaining the momentum of making progress in health and development. Climate variability is already a threat to the sustainability of water supplies and sanitation infrastructure.
Floods are ―normal‖ occurrences that continue to cause shocks for the affected population and to challenge water and sanitation managers. In many places they are likely to become more frequent with intensification of climate change, thus;
- Floods can have catastrophic consequences for basic water and sanitation infrastructure. Such damage can take years to repair.
- On a smaller scale, drinking-water infrastructure can be flooded and be put out of commission for days, weeks or months.
- Where flooding of sanitation facilities occurs, there may not only be a break in services, but the resultant flooding may distribute human excreta and its attendant health risks across entire neighbourhoods and communities.
Droughts occur unpredictably, worldwide. In many places they are likely to become more frequent and more widespread with climate change. For example:
- Falling groundwater tables and reduced surface water flows can lead to wells drying up, extending distances that must be travelled to collect water, and increasing water source pollution. In response, drilling rigs – which would otherwise be used to increase access – may be redeployed to renew or replace out-of-service wells, slowing the actual progress in extending access
Since climate change is likely to affect water sources and infrastructure in Tanzania and therefore it must be taken into consideration in design operation and maintenance of water and sanitation infrastructure or projects. Globally, climate change studies are coordinated by the United Nations Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC). Accordingly, designers should therefore use the latest information, data and model predictions available and include a statement on what measures, if any, have been allowed for in order to cope up with the climate change within the time frame of their project design (i.e. design life).
Potential Impacts of Climate Change on Water Supply Projects
It is emphasized that immediately the project is conceived, hydrological, rainfall and other meteorological data collection must be initiated. In addition and given the long design life of such structures, consideration must be given to the possible impacts of climate change.
IPCC (2014) indicated that human influence on the climate system is clear and recent anthropogenic emissions of greenhouse gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems. Climate change impacts the hydrological cycle resulting into changes in spatio-temporal distribution and magnitude of climatic variables such as temperature and precipitation. Changes in precipitation combined with rising temperatures, may adversely influence the availability of water, streamflow, soil moisture, the occurrence of droughts (Li et al., 2018; Asadieh and Krakauer, 2016) and flow regimes for freshwater ecosystems.
Climate models are needed in order to estimate the future climate. These models include a 3-dimensional representation of the atmosphere, land surface, sea, lakes and ice. The atmosphere is divided up into a 3-dimensional grid over and above the earth's surface. In order to obtain a good result, the models have to take the whole atmosphere into consideration, covering the entire surface of the earth as well as up into the air above it. These models are called global climate models (GCMs). The climate model calculations are based on emission scenarios or radiation scenarios. Emission scenarios are assumptions about future emission of greenhouse gases (GHGs), based on estimates of the development of the world economy, population growth, globalisation, increasing use of green technology, etc. The amount of greenhouse gases that are emitted depends on global evolution. These scenarios are called SRES scenarios (Special Report on Emission Scenarios (Nakićenović, 2000)). Radiation scenarios are based on assumptions about how the greenhouse effect will increase in the future, known as radiative forcing (measured in W/m²). If there is an increased emission of greenhouse gases, then there will be more radiative forcing. These scenarios are called RCP scenarios (Representative Concentration Pathways (Moss et al., 2010)).
The sources of emissions are the following with the energy sector/production remains the primary driver of GHG emissions: energy sector (35%), agriculture, forests and other land uses (24%), industry (21%), transport (14%) and building sector (6.4%) as per 2010 GHG emissions (IPCC, 2014). Projections indicates continued emissions of greenhouse gases will cause further warming and changes in the climate system. The following are among potential impacts of climate change: food and water shortages, increased displacement of people, increased poverty and coastal flooding.
During the climate negotiations in Cancún, Mexico 2010 there was an agreement in an ambition to limit the increase in global average temperature to below 2 degrees compared to pre-industrial (1881-1910) levels. A temperature increase of more than 2 degrees is a limit that is considered to be too costly on society and environment (e.g. IPCC, 2007; UNFCC, 2010), but still possible to be below (IPCC, 2014). In 2015 the countries of the world agreed on the so called the Paris Agreement. This states that the global temperature rise should be kept well under 2 degrees and that efforts should be made to limit the temperature increase even further to 1.5 degrees above pre-industrial levels.
Since the global temperature increase of 1.5 or 2 degrees are just averages it is interesting to look at the temperature increase at regional and local scales in Tanzania. Note that in the maps to show the patterns, future warming is compared to the period 1971-2000. Some of the warming occurred before year 1971. To be precise, the global average temperature had already increased by 0.46°C from pre-industrial time until 1971. A warming of 2 degrees compared to pre-industrial levels corresponds therefore to a warming of 1.54°C compared to 1971-2000 (Vautard et al., 2014).
Apart from temperature and precipitation, a number of climate indices are also calculated, with the help of the general meteorological parameters generated by the model. This could be the number of warm or cold days, accumulated precipitation during a week, or the length of the vegetation period. This climate change analysis uses four scenarios generally as used by IPCC, AR5:
- RCP2.6: Powerful climate politics cause greenhouse gas emissions to peak in 2020. The radiative forcing will reach 2.6 W/m² by the year 2100. This scenario is closest to the ambition of the Paris Agreement.
- RCP4.5: Strategies for reducing greenhouse gas emissions cause radiative forcing to stabilise at 4.5 W/m² before the year 2100.
- RCP8.5: Increased greenhouse gas emissions mean that radiative forcing will reach 8.5 W/m² by the year 2100. This scenario is closest to the currently measured trends in greenhouse gas concentrations.
The reference period 1961-1990 was widely used to define the current climate. New observations are compared to the mean value for 1961-1990 to measure how they differ. For example, if the summer is warmer than normal, it means that it is warmer than the average value of the summers of 1961-1990. The World Meteorological Organization, WMO, defines the reference periods, and the next reference period will be 1991-2020 which will start to be used in 2021. Climate scenarios are often presented as changes compared to the current climate. Often the reference period 1961-1990 is used, just as for observations. Since the climate is changing, the period 1961-1990 is not fully representative of what we consider to be the current climate. Therefore, later reference periods have started to be used, and many projects are now using the years 1971-2000.
An ensemble is a collection of climate scenarios (estimates of the future climate) where the individual scenarios are different from each other. The climate scenarios can for example differ with respect to the climate model used, or the emission or radiation scenario. A climate scenario that is part of an ensemble is called a member. An ensemble gives a good overview of the spread of the difference between the members, and highlights some of the uncertainties associated with simulating the future climate. The ensemble is a measure of the reliability of the results. If many different climate scenarios give similar results, then the results are relatively more reliable than if they all pointed in different directions.
A global climate model can perform well in some parts of the world and less well in other areas. Another model may be describes the temperature well but is not as good for precipitation. It can therefore be worth using large ensembles since they are better at capturing the uncertainty of the results. In practice, the choice of the ensemble run depends very much on how many model simulations can feasibly be run. When an ensemble run has been carried out, the spread of the result gives an idea about the reliability of the results. Depending on the type of ensemble that has been produced, the significance of the choice of climate models and start values can be studied.
Future increase in precipitation extremes related to the monsoon is very likely in Africa. Monsoons are the most important mode of seasonal climate variation in the tropics (i.e. tropical continents: Asia, Australia, the Americas and Africa), and are responsible for a large fraction of the annual rainfall in many regions. In Africa, monsoon circulation affects precipitation in West Africa where notable upper air flow reversals are observed. East and south African precipitation is generally described by variations in the tropical convergence zone rather than as a monsoon feature.
The African continent encompasses a variety of climatic zones. The continent is divided into four major sub-regions: Sahara (SAH), Western Africa (WAF), Eastern Africa (EAF) and Southern Africa (SAF). Also, tropical cyclones impact East African and Madagascan coastal regions and extratropical cyclones (ETCs) clearly impact southern Africa. The East Africa experiences a semi-annual rainfall cycle, driven by the Inter-tropical Convergence Zone (ITCZ) movement across the equator. Direct links between the region‘s rainfall and El Nino-Southern Oscillation (ENSO) have been demonstrated (Giannini et al., 2008), but variations in Indian Ocean Sea Surface Temperature (SST, phases of the Indian Ocean Dipole - IOD) are recognized as the dominant driver of East African rainfall variability (Marchant et al., 2007). Indian Ocean Dipole (IOD) is defined by the difference in sea surface temperature between two areas (or poles, hence a dipole), leading to (i) a western pole in the Arabian Sea (Western Indian Ocean), (ii) an Eastern pole in the Eastern Indian Ocean South of Indonesia. Variability in Southern Africa‘s climate is strongly influenced by its adjacent oceans (Rouault et al., 2003; Hansingo and Reason, 2008, 2009; Hermes and Reason, 2009) as well as by ENSO (Vigaud et al., 2009; Pohl et al., 2010).
The IPCC (2013) for CMIP5 projections under RCP4.5 indicate that for the East African region the predicted increase in temperature is between 0.5°C and 1.2°C, 1.0°C and 2.4°C and 1.0°C and 3.1°C for 2035, 2065 and 2100 respectively annually. The predicted increase in precipitation is between -5% and 10%, -6% and 17% and -7% and 21% for 2035, 2065 and 2100 respectively annually. This implies that the East African region will get more rain but become drier as temperatures rise and evapo-transpiration increases. Therefore, water supply and sanitation designs should anticipate the potential impacts on water sources and infrastructure, and therefore inform on water resilience or water security aspects during the project design life. Also, seasonal precipitation change (mm) in East Africa for 2011-2040 (2020s), 2050s (2041–2070) and 2080s (2071–2100) with the baseline period 1961– 1990 as predicted by the GCMs with Statistical Downscaling Model (SDSM) indicated that in Tanzania, large rains (Masika, in MAM) will get smaller, up to -500 mm and small rains (Vuli, in OND) will increase a little for all RCPs 2.6, 4.5 and 8.5 (Gebrechorkos, et al., 2019).