Thursday, August 19, 2010

Extreme weather and society

(first published on the commoditywx blog)
For meteorologists, weather and climate are always top of mind.  From the time we arise each day, through the last moments before our eyes close for at least a few hours in the evening (or following morning), most of our thoughts are consumed trying to make some sense of the behavior of the atmosphere and the fluid layer enveloping the planet.  Whether it be sea surface temperatures and their relationship to cyclogenesis in Asia, or the influence of wintertime snowpack on spring runoff and water availability for North American farmers, there is always something interesting to think about and to learn from.  In addition, many of us in both the private and public sector try to take this knowledge one step further, and apply it to the benefit of society.  While we make the case on a regular basis that one would be hard pressed to find a sector of modern life that is not in some way influenced by weather, lately, our profession has not had to do much in the way of convincing.  From the potential impact of tropical storms on oil dispersion in the Gulf of Mexico, to floods causing massive humanitarian crises in Pakistan, to heatwaves and wildfires which have contributed to both a doubling in Moscow's death rate to a virtual standstill in the city's economy, weather is now on nearly everyone's mind.
Therefore, this article will discuss some of the current extreme weather that has affected different parts of the world, and in the process, hopefully it will shed some light on the physical processes that contributed to these events.  What the article will not do is attempt to assign broad causes to acute events - for example, many of the questions that we receive on a daily basis deal with the desire to know immediately if a particular event is related to natural or man-made disturbances.  While we may speculate on the potential for specific causal mechanisms, the only honest way to answer that question is to say that we really do not know.  These anomalous weather events may be isolated occurrences, while they may also be part of a longer term trend related to decadal or multi-decadal cycles or external influences.  Regardless, weather always has and always will exhibit what appear to be extremes, and when looking at these extremes in the context of history, the disturbances that we are currently experiencing may be considered somewhat mild.  Not discounting the massive disruptive power of a hurricane or flood, the seemingly devastating nature of these events may be more related to the precarious relationship between humans, the atmosphere and civil infrastructure, which given the complexity of regional and global settlement patterns and their related economies, is perhaps more tightly coupled today than in any other time in history.
Over the last two weeks, even with only a casual perusal of the news, it would be difficult to escape noticing how extreme weather has caused great disruption to many lives.  In this post, the discussion will focus on highlighting some (not all) of the causes related to the weather disasters which are currently affecting large numbers in Russia and Pakistan.  We will see that while they are separate events, there are some common physical factors.
Russian Heat Wave
Global wheat futures have spiked over the last week with much of the activity stemming from potential crop losses in Russia.  Stories of parched fields and decimated crops are everywhere.  However, while the market reaction was rapid, this story has been building for several months.  To be fair, part of the price spike came on the heels of a Russian export ban, but nonetheless, this story had a weather origin.  The four maps below show the monthly year over year (2010 vs. 2009) changes in maximum temperature and precipitation for June and July.   The current weather this week is not much better, as temperatures in and around Moscow are making the mini-heatwaves in the US seem trivial.

One of the causes for the maximum temperatures to stay so hot for so long has been a persistent high pressure system centered over Eastern Europe, coupled with changes in the pattern of the jet stream.  When this high is as entrenched as it has been, it serves to do two things: (1) it diverts a jet that would normally bring with it cooler air into the region, steering this cooler air into parts of central Russia and northeastern Africa.  It also (2) blocks moist air from the southeast as well, which is exacerbating the dryness - this is also one of the reasons that parts of central Africa are seeing better moisture in recent months.  In addition, there is an active west to east jet stream that travels above western Russia, which typically exhibits a seasonal shift to the east, and in the process allows moister air from the west to migrate into the region; this July, the jet did not shift, and the result was a prolonged period of moisture-free air.  When this combines with a strong high, the region experiences weather like it has seen over the last month.  And when there is a high pressure system in one region, there is often a corresponding low elsewhere.
Flooding in Pakistan
The low in this case, has been over the mountainous region over northern Pakistan.  And this cold low has been the catalyst for a good portion of the excess rains.  So, while located in distinct climatic zones, the heat and dryness in Russia has a connection to the floods in Pakistan.  But there is more to this puzzle.  Every year, the annual Indian Monsoon is eagerly anticipated throughout India and Pakistan, as much of the commercial activity that takes place in both countries is agrarian in nature, and therefore, dependent upon healthy seasonal rains.  In 2009 the monsoon was deficient, leading to short crops in many sectors, so the arrival of the rainy season this year carried a heightened importance.  The onset of the 2010 monsoon was healthy and most regions have been receiving beneficial moisture totals, but the placement of another area of high pressure over northeast India has, thus far, kept northern states in India dry; in the process, this high has been diverting even more moisture which flows from southeast to northwest into central/western India along into Pakistan.  The first map below from NOAA's Earth System Research Laboratory depicts the storm tracks from the last week (as viewed via anomalies in outgoing longwave radiation), where the excess moisture is visible directly over Pakistan.  The second map below (from the NOAA Climate Prediction Center) highlights wind anomalies over the last week, and we see from this map that the stronger winds originating from the southeast were actively driving the moisture into areas that needed it the least.

Making the rainfall situation for Pakistan worse is the condition of drainage infrastructure, which are silt-laden, so when excess rains fall, it takes much longer to drain than should be needed.  Unfortunately, any excess rains in the coming weeks will likely be met with more problems for civilians.  As of today (11 Aug) estimates on the number of flood related deaths are at around 1300, with over 14 million having been affected by the floods.  Both of these figures are expected to rise.
In the months to come, in addition to the normal commentary posted here which focuses on issues at the weather/commodity nexus, Weather Trends will now start to include discussions related to global weather phenomena that sit at the broader interface of weather, climate and society.  As the last couple of years have seen a heightened interest in this area from the research side, evidenced by new topics and sessions present at the annual conferences hosted by the American Geophysical Union, the American Meteorological Society, and others, we will hope to bring some of these discussions to a broader audience, where readers might not otherwise be privy to the discussion.  We also hope that it will launch new dialogue, where readers become aware how closely related their lives and decisions are to weather and climate.

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