22.8 percent in 2000 to 23.5 percent and 24.6 percent by 2020, respectively, for the lower and upper bound climate change scenarios under the above assumptions.

The total number of diarrhea cases in children under age five would consequently increase by about 46 percent, from 26 million cases in 2000 to 38 million cases in 2020 in the upper bound scenario. The increase in diarrheal cases between 2000 and 2020 can be decomposed into two factors: the increase in diarrheal incidence as a result of the increased frequency of excess rainfall and rises in extreme temperature, and the increase in population under the age of five<sup>6</sup> Our calculation shows that population growth would account for 36 percentage points of this increase and the increased frequency of extreme events would contribute about 9 percentage points.

The potential health cost of diarrhea is illustrated through the calculation of the number of disability adjusted life years (DALYs). The calculation of DALYs attributable to diarrheal disease for children under the age of five is the sum of morbidity and mortality from diarrhea.

Morbidity is estimated from the total diarrheal cases for any given year, assuming the average length per episode is four days, DALY disability severity weight of 0.11 and DALY age weight of 0.31 from WHO guidelines (Murray and Lopez, 1997). Mortality is calculated based on total diarrheal cases for any given year, estimated conditional mortality probability (3.7 %)7 and discounted years of life lost per child from WHO guidelines. Using the predicted diarrheal incidence from our sample (see Table 5), the health burden of diarrhea among children under the age of five is about 33.5 million DALYs for 2000, which is very close to the WHO estimate of about 32.2 million DALYs for 2005 for Sub-Saharan Africa (WHO, 2008).

The economic costs of diarrhea are also presented in Table 5. The share of total health cost of diarrheal diseases in the under five age group is the ratio of DALYs multiplied by GDP per capita to total GDP for the corresponding years.8 The ratio of health cost to GDP, as shown in footnote 8 is determined principally by three factors, the population age structure (ratio of population under age five to total population), the diarrheal incidence and the conditional under five mortality probability. The estimation results presented in Table 5 show that the economic costs of diarrheal disease relative to GDP

> 6 Δ diarrheal cases between 2000-2020

= POP2020 * DI 2020 – POP2000 * DI 2000 = POP2020 * Δ DI + Δ POP * DI 2000 where DI refers to diarrheal incidence.

7 The probability of under-5 death from diarrhea is estimated using the formula: Prob(death/diarrhea)=prob(death caused by diarrhea)/prob(diarrhea). The probability of diarrhea caused death is estimated using the WHO cause of death information for Sub-Saharan Africa in 2002. The estimated diarrheal incidence is from our own estimates using the DHS data for Sub-Saharan Africa. 8 Health cost/GDP = (DALY * GDP per cap)/ Total GDP = (Mortality DALY + Morbidity DALY) * GDP per cap)/ Total GDP = [(prob(death caused by diarrhea)*pop_4*DI*Φ+ pop_3*DI*Ψ]* GDP per cap)/ Total GDP, where DI is the diarrheal incidence = (Pop_4/Total pop)*{[(prob(death caused by diarrhea)*Φ+ DI*Ψ]}, where Φ and Ψ are fixed coefficients for disability weight, age weight and discounted years of life lost taken from WHO.

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