Elsevier

Environment International

Volume 31, Issue 8, October 2005, Pages 1167-1181
Environment International

Review article
Climate change and changes in global precipitation patterns: What do we know?

https://doi.org/10.1016/j.envint.2005.03.004Get rights and content

Abstract

The objective of this paper is to synthesize the large literature recording changing patterns of precipitation in the observed data, thus indicating that climate change is already a reality. Such a synthesis is required not only for environmental researchers but also for policy makers. The key question is the broad picture at major regional and continental levels. Some interesting conclusions for this survey are emerging. For example, the review shows increased variance of precipitation everywhere. Consistent with this finding, we observe that wet areas become wetter, and dry and arid areas become more so. In addition, the following general changing pattern is emerging: (a) increased precipitation in high latitudes (Northern Hemisphere); (b) reductions in precipitation in China, Australia and the Small Island States in the Pacific; and (c) increased variance in equatorial regions. The changes in the major ocean currents also appear to be affecting precipitation patterns. For example, increased intensity and frequency of El Niño and ENSO seem associated with evidence of an observed “dipole” pattern affecting Africa and Asia, although this time series is too short so far. But the changing pattern calls for renewed efforts at adaptation to climate change, as the changing precipitation pattern will also affect the regional availability of food supply.

Introduction

With the recent ratification by Russia, the Kyoto Protocol came into force as a global treaty, binding its signatories to the reduction of greenhouse gases as set out in the Protocol, though the United States and Australia remain outside this fold. Nevertheless, the ratification shows that a global commitment to take some action to mitigate global climate change under the general framework the United Nations Framework Convention on Climate Change is finally underway, with further amendments and tightening of harmful emissions now a real possibility. Most climate change scientists are hoping that further international action may mirror the actions taken after the initial signing of the Montreal Protocol, which was followed by a number of additional amending agreements. Thus, there is much hope that Kyoto may be the start of a similar process. However, a series of scientific studies and number of press reports show that climate change is well underway. While the subject of climate change is vast, there is at least one topic within climate change that deserves urgent and systematic attention, and that is the changing pattern of precipitation around the world. If climate change is already underway, how is it affecting observed precipitation? The objective of this paper is to synthesize the vast literature on the changing pattern of observed precipitation and to discern some general patterns at major regional and continental levels. Some interesting conclusions for this survey are emerging. For example, one systematic result is increased variance of precipitation everywhere. Consistent with this finding, we observe that wet areas become wetter, and dry and arid areas become more so. In addition, the following general changing pattern is emerging: (a) increased precipitation in high latitudes (Northern Hemisphere); (b) reductions in precipitation in China, Australia and the Small Island States in the Pacific; and (c) equatorial regions become more variable, i.e., increased variance. The changes in the major ocean currents also appear to be affecting precipitation patterns. For example, increased intensity and frequency of El Niño and ENSO seem associated with evidence of an observed “dipole” pattern affecting Africa and Asia, although this time series is too short so far. But the changing pattern calls for renewed efforts for adaptation to climate change, as the changing precipitation pattern will also affect the regional availability of food supply.

Increasing global surface temperatures are very likely to lead to changes in precipitation and atmospheric moisture because of changes in atmospheric circulation, a more active hydrological cycle, and increases in the water-holding capacity throughout the atmosphere. The El Niño-Southern Oscillation (ENSO) is the primary global mode of climate variability in the 2- to 7-year time frame. El Niño is defined by sea surface temperature (SST) anomalies in the eastern tropical Pacific, while the Southern Oscillation Index (SOI) is a measure of the atmospheric circulation response in the Pacific–Indian Ocean region. Both the activity and periodicity of ENSO have varied considerably since 1871 with considerable irregularity in time. There was an apparent “shift” in the temperature of the tropical Pacific around 1976 to warmer conditions, which appeared to continue until at least 1998. During this period, ENSO events were more frequent, intense or persistent. ENSO has been related to variations of precipitation and temperature over much of the tropics and sub-tropics, as well as some mid-latitude areas. All this evidence needs to be systematically synthesized and integrated to see what global picture emerges. This paper is a first attempt to do that.

This paper is organized as follows. Section 1 considers the changing pattern at a synoptic level: land areas with mid- and high latitudes and the tropics, followed by the oceans. Section 2 covers the growing evidence of climate variability and extremes. Section 3 is a more detailed breakdown by regions and main continents. This is followed by some concluding remarks.

Section snippets

Land

Overall, global land precipitation has increased by about 2% since the beginning of the 20th century (Jones and Hulme, 1996, Hulme et al., 1998). The increase is statistically significant, though neither spatially nor temporally uniform (Karl and Knight, 1998, Doherty et al., 1999). Dai et al. (1997) found a global long-term increase in precipitation separate from ENSO and other modes (patterns) of climate variability.

Climate variability and extremes

Groisman et al. (1999) developed a simple statistical model of the frequency of daily precipitation based on the gamma distribution. They applied this model to a variety of regions around the world (40% of the global land area) during the season of greatest precipitation. Although Wilks (1999) shows that the gamma distribution under some circumstances can underestimate the probability of the highest rainfall amounts, Groisman et al. (1999) applied the distribution to the upper 5 and 10

The 1997–1998 ENSO event

ENSO appears to play a major role in East Africa, but it masks the perhaps more important role of the other oceans, particularly the Indian Ocean. The 1961–1962 rains were spectacularly manifested as rapid rises in the levels of east African lakes. Lake Victoria rose 2 m in little more than a year (Flohn and Nicholson, 1980). This was not an ENSO year, but exceedingly high SSTs occurred in the nearby Indian Ocean as well as the Atlantic. Such high SSTs are associated with most ENSO events, and

Conclusions

Annual land precipitation has continued to increase in the middle and high latitudes of the Northern Hemisphere (very likely to be 0.5% to 1% per decade), except over Eastern Asia. Over the sub-tropics (10°N to 30°N), land-surface rainfall has decreased on average (likely to be about 0.3% per decade), although this has shown signs of recovery in recent years. Tropical land-surface precipitation measurements indicate that precipitation has probably increased by about 0.2% to 0.3% per decade over

Acknowledgements

I am grateful to the anonymous referees and the Editor of this journal for their constructive comments on an earlier version. However, the views expressed here are those of the author alone. This research was funded by the Canadian Water Network.

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