«DIPLOMA THESIS Linking Climate Change with Food Security in the highlands of Khyber Pakhtunkhwa, Northwest Pakistan Presented by: Martin Kienzler ...»
More interesting especially for agricultural questions are the seasonal precipitation patterns (see ﬁgure 6.11). In spring when the monsoon depression does not develop at all over the Indian subcontinent, most parts of Pakistan are extremely dry. South of around 32◦ northern latitude precipitation does not exceed 50 mm at all during these three months, not even in the mountain ranges of Beluchistan. A diﬀerent situation reveals the northern part of the country. Especially in the northwestern areas a considerable portion of annual rainfall occurs during these three months and precipitation amounts add up to more than 500 mm in some areas. This is due to the western disturbances. In summer a diﬀerent picture is drawn. Now all parts of Pakistan south of the Himalaya receive the highest precipitation of all year. Especially the mountain regions of the Sulaiman range and the Indus plains north of 30◦ latitude can record rainfall amounts of more than 200 mm while the foothills and high mountain areas of the Himalaya receive even more than 500 mm during this period. In contrast all the regions beyond the ranges of the Himalaya and southern Hindu Kush are shaded from the monsoonal rains and therefore almost get no rain at all. For example in northern Khyber Pakhtunkhwa less than 30 mm per month occur in summer. Most parts of Afghanistan are completely dry during summer. Even the high mountain ranges of the Karakoram only receive little precipitation.
Figure 6.11 – Mean seasonal precipitation over Pakistan after the REMO model output.
MAM = spring, JJA = summer, SON = autumn and DJF = winter.
the Sulaiman and coastal mountains fall dry again, while the northern Indus plains still receive considerable rainfall of up to 200 mm. The regions north of the Himalaya get little more precipitation than in summer, but the bottom of the valleys stay relatively dry. The Himalaya itself and its foothills now receive the fewest rain of the year, which however still is more than 300 mm during these months. When winter starts and western disturbances aﬀect the northwestern part of Pakistan within the Hindu Kush, it begins to receive more precipitation again. So do the high mountain areas of Karakoram and Himalaya, too, except the deep valleys in between like around Gilgit. For all other parts of Pakistan south of around 33◦ North the driest time of the year begins until monsoon starts again.
Chapter 6. Results
6.2.2 Trends Similar to the variable temperature also for precipitation a serial data curve was generated to illustrate the development of precipitation amounts of Khyber Pakhtunkhwa for the period 1901 to 2009. Again a mean value of all the 55 grids displayed in ﬁgure 4.1 was calculated for each year quasi to get a value of annual mean precipitation of Khyber Pakhtunkhwa. These values alongside an 11-year running average (blue line) are shown in ﬁgure 6.12.
The course of precipitation during the twentieth century shows high variability, the mean annual precipitation of Khyber Pakhtunkhwa varies between 350 and 800 mm.
The ﬁrst half of the century is characterised of a constant variation around a mean of around 500 mm. The 11-year running average is more or less constant throughout the ﬁrst ﬁfty years of the century. But suddenly around 1950 precipitation generally tends to rise, reaching maximum values around 1960. The next ten years are marked by lesser but still above-average rainfall amounts before there is an increasing tendency again.
The eighties and early nineties represent the wettest period of the last 109 years besides the peak around 1960. Since around 1995 precipitation amounts rather tend to decrease again.
Figure 6.12 – Mean annual precipitation averaged over Khyber Pakhtunkhwa, 1901-2009.
Blue line = 11-year running average Data obtained from Jones & Harris (2008) The calculation and interpretation of linear trends for precipitation turns out to be more diﬃcult as it is for temperature. This is because precipitation is a far less predictable variable and trends depend a lot more on extreme events (see chapter 7). But anyway the results of a trend analysis shall be demonstrated in this section and discussed in the next chapter.
Chapter 6. Results
Figure 6.13 shows the linear trend for the period 1971 to 2000 on an annual scale. It is obvious that the results of the two diﬀerent datasets do not match with each other in every region. According to the CRU data a reduction of annual precipitation amounts during this period is clearly visible for most parts of the country. It is strongest within the eastern part of the Himalayan foothills, in the southern part of the Sulaiman range and along the coast of the Arabian Sea near the estuary of the Indus river. Here rainfall amounts are supposed to decrease at a rate of 100 to 150 mm per century, even though annual rainfall is not more than 200 mm. In the central parts of southern Pakistan the reduction is not as strong and some small areas even show positive trends. For most of Khyber Pakhtunkhwa and the northeastern part of Kashmir it is the other way round. Precipitation trends are distinctly positive, especially in the west along the Afghan border. A plus of up to 200 mm per century is recorded. For the two case studies the following is valid: The surroundings of Chitral show an increasing trend of around 100 to 150 mm per century, which is almost 30% of the annual rainfall. The valley of Kaghan is situated within a region of decreasing precipitation. The rate is less than 50 mm per year, which is only around 5% of the annual amounts. Both observations are not signiﬁcant at the 95%-level. In contrast REMO simulates a distinct increase of precipitation of more than 50 mm per century for all of Pakistan south of around 33◦ latitude. Similar to the CRU output the eastern part of Pakistan’s Himalaya shows clearly negative trends but mostly less than 100 mm per 100 years. For most of Khyber Pakhtunkhwa the results of the two datasets agree with each other, but somehow REMO generally simulates lesser trend rates. Thus for Chitral an increase at a rate of less than 50 mm per century is simulated, while precipitation in Kaghan valley is reduced at around 50 mm per century.
Figure 6.13 – Precipitation trend over Pakistan 1971-2000 for the whole year extrapolated to mm per 100 years.
Left: CRU data. Right: REMO model output. The black dots represent grids, which are signiﬁcant to 95% (α = 0.95)
Seasonal trends Regarding the trends of the summer months June, July and August the two datasets do not agree again. The CRU data record negative trends for the whole country, except the farthest North and Northeast and a small area in central Pakistan. The strongest decrease of precipitation is recorded in the South along the coast, in the eastern part of the country, in the Safed Koh range and along the monsoonal belt at the foothills of the Himalaya. Here, as well as along the elongation of the monsoon belt into India, rainfall seems to decline at a rate of more than 300 mm during the summer months, which is almost 50% of all summer precipitation. This would mean that the intensity of the Indian summer monsoon would diminish distinctly, a fact that has to be discussed in chapter 7. In contrast REMO simulates an increase of precipitation for most parts, especially for the areas along the lower section of the Indus river and for the western half of the country. The strongest increase is among others simulated for central Khyber Pakhtunkhwa. Only the eastern part of Pakistan’s Himalaya is supposed to show a strong negative trend in summer rain. For both case study areas only a slight increase of less than 50 mm per century is simulated. CRU records a slight increase at the same rate for Chitral but a clear precipitation reduction of around 100 mm per century for Kaghan, both observations are signiﬁcant at the 95%-level. (6.14) Figure 6.14 – Precipitation trend over Pakistan 1971-2000 for summer (JJA) extrapolated to mm per 100 years. Left: CRU data. Right: REMO model output. The black dots represent grids, which are signiﬁcant to 95% (α = 0.95) The development of winter precipitation is interesting, but again rather contradictory when comparing the results of the two datasets (6.15). Regarding the CRU output all of Pakistan south of 32◦ latitude is experiencing a slight negative trend, the rate increasing from west to east but nowhere being more than 75 mm per 100 years. The far North of the country, the Karakoram ranges and the southern part of the Pamir also show decreasing precipitation trends of between 50 and 100 mm per century. In contrast a broad belt
Figure 6.15 – Precipitation trend over Pakistan 1971-2000 for winter (DJF) extrapolated to mm per 100 years.
Left: CRU data. Right: REMO model output. The black dots represent grids, which are signiﬁcant to 95% (α = 0.95) extending from the upper half of the Indus plains to the main ranges of the Himalaya and spreading from west to east records a strong positive trend of 150 to 200 mm in the core. This means a growth of around 45% to 60% of the mean winter precipitation amounts in these areas. Kaghan valley lies within this core zone of a strong positive trend. For Chitral only a slight positive trend is recorded. Both ﬁndings are signiﬁcant at the 95%-level. For all of Pakistan south of 34◦ northern latitude REMO simulates slight positive precipitation trends. However in most parts they are less than 25 mm per year. Decreasing trends are simulated for a narrow belt along the 35th line of latitude and amount up to 200 mm per century in some areas. Further north of this belt there is again no visible pattern of trends and slightly increasing and decreasing trends alternate on a small scale. For central Chitral REMO simulates a slightly increasing trend of winter precipitation, while for northern Chitral a strong decreasing trend is likely. Similarly Kaghan valley is situated within a region of clearly reducing precipitation amounts.
6.3 Future projections The simulations of the regional climate model REMO enable us to throw a glance into the future development of climate in Pakistan.
To make a statement about future projections of temperature and precipitation, the mean values of the period 2071 to 2100 were compared to the means of the recent period 1971 to 2000. The diﬀerences of the averages are illustrated in ﬁgure 6.16 on an annual scale and in ﬁgure 6.17 for the diﬀerent seasons.
If looking at the development of the annual temperature values (left side of ﬁgure 6.16) it is obvious that over the whole area a warming of more than +4◦ C until the end of the twenty-ﬁrst century is projected. The warming pattern somehow seems to
Figure 6.16 – Diﬀerence of the 2071-2100 mean and the 1971-2000 mean for temperature (left, ◦ C per century) and precipitation (right, mm per century).
REMO model output follow the relief. So the low-lying areas in the South and along the Indus river show the fewest increase in temperature of +4.0◦ C to +4.75◦ C. A similar relatively slight warming is simulated for the mountain valleys in the Northern Areas like the Indus, Gilgit and Shyok river valleys. The high mountain ranges, especially of Himalaya and Hindu Kush in contrast are supposed to suﬀer strong warming of partly more than +5.5◦ C. Compared to global patterns this means an above-average warming for the mountain regions of Pakistan.
The right side of ﬁgure 6.16 shows the projected diﬀerences of future annual mean precipitation. Three distinct features become obvious: A centre of increasing precipitation can be sighted around the lower section of the Indus river between 27◦ and 29◦ northern latitude. Mean values are projected to be almost 100 mm above the present average.
Just west of this region near the coast of the Arabian Sea rainfall amounts seem to become less at a considerable rate. The second distinct feature is the development along the monsoonal belt. Here precipitation is supposed to be reduced clearly during the last third of the 21st century. In some parts rainfall amounts should decrease of more than 200 mm compared with present values. In contrast to this, a broad belt spreading parallel to the monsoon belt over the Karakoram and Pamir ranges is showing an opposing development: Here precipitation is simulated to increase of 150 to more than 200 mm in some areas. According to the REMO simulations the regions of the two case studies lie within moderately (Chitral) and strongly (Kaghan) reduced precipitation, respectively.
Both regions furthermore will suﬀer a strong warming of around +5.5◦ C.
More important from an agricultural point of view are changes in the diﬀerent seasonal means, which are illustrated in ﬁgure 6.17. Here, the left column shows the temperature development and the simulations for the precipitation averages are shown in the right column. The respective seasons are, from top to bottom, spring, summer, autumn and
Chapter 6. Results
winter. For most parts of the high mountain regions of the Hindu Kush and Himalaya the strongest warming is simulated for the winter and spring months. In contrast especially the summer months denote rather moderate warming. The same is true for the areas around the two case studies. Only the highest areas of the Chitral district seem to suﬀer a strong warming during summer, too. For the low-lying areas of the Indus plain and the southern part of Pakistan along the coast it seems to be oppositional: The strongest warming is simulated to happen in summer, while the winter months are characterised by a relatively moderate increase in mean temperatures.