A climate expert's take on Pakistan's floods

What is happening in Pakistan cannot be described in a single word – like disaster or catastrophe. We are watching a combination of climate, weather, population, societal capacity, and geopolitics whose scope and ramifications are far beyond a “historic flood.”

I do not have any special insight, but I do have a special interest. My youngest sister Elizabeth is in Peshawar on the front line of the flood. She is the “friend” that Jeff Masters referred to in his blog on August 10, 2010. (As picked up in the NYTimes.) And with this personal interest, I find myself digging around sources of local Pakistani news. What we are watching has all of the elements of climate disaster of the type that is predicted to be more common in the future. Let’s deconstruct this.Climate and climate change: The weather that has brought all of the rain to Pakistan (and India and China) is associated with the South Asian Monsoon. This is the flow of air from the Indian Ocean into South Asia with large amounts of rain released when the air flows up the high topography that defines Central Asia. In Pakistan it is often what is called the northwest extension of the monsoon, which happens later in the season than the monsoonal flow that brings rain to South India. What is happening, and it is still going on, is an extreme event of an important and well described element of the Earth’s climate. From the point of view of meteorological measurements, this year’s rains and floods might be “historic” in the sense of being largest. I will let those who are more familiar with records argue that point; it does not really matter. (I am preempting any consideration of any relevance of the statement “but there was a big event like this in 18xx as described by, say, Charles Napier.”)The prediction of “more extreme weather” is part of the portfolio of events associated with the predictions of global warming. Warmer ocean, warmer air, more water in the air—it still gets cold as it flows up the mountain and it rains. So the getting-to-be-old scientific hedge of “this is consistent with the predictions of global warming” is true.Can we attribute this particular event to global warming? Probably not, but let’s think about it. One of the papers in my collection of important papers is one by P . Frich. This paper talks about indices that measure climate extremes and sets out the arguments about seeing not one isolated extreme, but a whole set of extremes. This taken in concert with changes in the average (a trend) and more and more extremes as time goes by, leads to a situation where it is extremely unlikely that all of the extreme events can just be normal chance. Look at the extreme events—first the drought and fires in Russia, perhaps the heat in the eastern U.S., add in the cool warm season in Southern California (to be replaced by extreme heat), we are seeing coherent behavior that is, again, consistent with the predictions of global warming. (See Peter Stott.)Attribution of the 2010 monsoon and flood to “global warming” will be left to far more sophisticated arguments and time. We see here an extreme climate event, hard to ascribe this to “weather,” in a place with highly vulnerable people, in a country with low “resilience” to such an event. (What country could respond to 20% of its surface being flooded and 20,000,000 people displaced?) This type of event will occur again, whether or not this particular event is attributed to global warming. With global warming, they will occur more frequently, perhaps be more extreme. Pakistan will need to rebuild, to redevelop, to develop, and the smart redevelopment will realize that these events will happen again, and build in extra because it will happen more often.

Continue reading professor Rood’s complete blog entry at www.wunderground.com


  1. Bob Spink - 1969

    This is what is known as weather. It is unpredictable, widely variable, and quickly changes. It always has and always will.


  2. hans rosendal - 1965

    The devastating floods of the Indus River Valley occurred shortly after an Arabian Sea tropical cyclone affected the same general area. Availablity of soil moisture may have contributed to pushing NWward the sharp boundary between moist monsoon weather to the east and dry subsiding air to the west. Flow aloft is very weak and anticyclonic at upper tropospheric levels, and recycled soil moisture has a way of remaining within the region for an extended period. I have experienced the same effects in Arizona after the first wetdown of the monsoon season. The blocking High over European Russia caused a cutoff Low or troughy branch of the upper jet down across the Middle East inducing anticyclonicity and divergent flow aloft (along with inertial instability) along the anticyclic side of the jet and along the midlevel zero relative vorticity line. The effect of the upslope low level moist and cyclonic (shear vorticity mainly) flow in setting off and sustaining the precipitation is off course very important. Just my take on it for what it is worth. Hans


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