Global Environmental Change Research Pathways for the Next Decade (1999) / Chapter Skim
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3 Changes in the Climate System on Seasonal to Interannual Timescales
3 Changes in the Climate System on Seasonal to Interannual Timescales
Pages 87-126
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From page 87... ...
We have already begun to predict aspects of El Niño in the tropical Pacific. These forecasts are used by the affected countries (Peru, Brazil, Australia, Chile, Columbia, the Philippines, and the American Flag Pacific Islands)
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From page 88... ...
In particular, better prediction of precipitation is of special interest because it can change the way people interact with the environment, perhaps in revolutionary ways. Precipitation is a fundamental determinant of climate and human habitability through its relationship to land surface conditions, including soil moisture, snow cover, vegetation, evaporation, stream discharge, and surface temperature.
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From page 89... ...
The case study in northeast Brazil highlights the significance of climate prediction capability for an agrarian society. Learning to apply seasonal to interannual climate predictions well, for the benefit of human society, is an important research imperative, but it is not directly addressed here.
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From page 90... ...
TAO telemeters back the data on winds and upper-ocean thermal structure to the Global Telecommunication System, from which it is available to all.a A 1996 report provides a complete history and extensive references.4 Macroscale Climate Variability and Crop Yields in the Monsoon Regions The annual cycle of the monsoon systems has led the inhabitants of monsoon regions to divide their lives, customs, and economies into two quite different phases: the "wet" and the "dry." The wet phase refers to the rainy season, during which warm, moist, and very disturbed winds blow inland from warm tropical a A picture of conditions for the tropical Pacific yesterday is available at http://www.pmel.noaa. gov/toga-tao/realtime.html.
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From page 91... ...
This distinctive variation of the annual cycle occurs over Asia, Australia, western Africa, and the Americas. In some locations (e.g., the Asia-Australia sector)
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From page 92... ...
Generally, warm events in the tropics are associated with deficient rainfall, while cold events appear to be related to abundant rainfall. The relationship between ENSO conditions and the Indian rice yield suggests a number of questions: • Although the relationship between ENSO conditions and Indian rice yield is not perfect, it is regular enough to raise the tantalizing suggestion that macroscale variations in the climate system influence variability on the
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From page 93... ...
AIRI and crop production relationship, depending on their values' percent deviation from the mean, CHANGES IN THE CLIMATE SYSTEM ON SEASONAL TO INTERANNUAL TIMESCALES and (b) relationship between AIRI and preceding winter SOI index.
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From page 94... ...
In the preceding discussion, Indian crop yield is used as an example of the importance of discerning the ways that macroscale climate variability affects the local scale. The questions raised above are common to the monsoon regions of Australia, Africa, and the Americas.
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From page 95... ...
The entire scenario would be reversed when winter and spring Eurasian snows are below normal precipitation. General circulation modeling sensitivity experiments substantiate observational evidence of an inverse snow-monsoon relationship.12 In analyzing the relative role of SST variations and land surface processes on the interannual variability of the Asian monsoon system, it is recognized that the former plays a dominant role.
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From page 96... ...
Modeling experiments carried out in the context of the Global Energy WaterCycle Experiment Continental-Scale International Project (GCIP) -- specifically using the Atmospheric Model Inter-Comparison Project's 10-year runs -- show that it is possible to provide improved simulation of the mean annual cycle when soil moisture is specified.
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From page 97... ...
Nonetheless, these AMIP simulations suggest that improved specification of soil moisture, and, it might therefore be presumed, improved prediction of the seasonal evolution of soil moisture in coupled terrestrial hydrological-atmospheric models, have the potential to improve seasonal precipitation forecasts. Dynamical processes controlled by regional water and energy balance can influence vapor flow and in this way may contribute to the occurrence of extreme events.
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From page 98... ...
Simulations carried out at the European Centre for Medium-Range Weather Forecasting (ECMWF) used two land surface schemes -- one with known defects and another with model improvements correcting those defects such that regional-scale soil moisture fields were better represented in the model.23 Predictions made with the version that more poorly represented surface interactions, and thus calculated overly dry soil moisture, provided an unrealistic simulation of the 1993 Mississippi River floods.
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From page 99... ...
What limits the skill of ENSO predictions now? Relatively skillful forecasts of SST in the tropical Pacific are now being made at lead times of one year, with indications of predictive skill for up to two years in advance.29 It is of great interest to know if there is an ultimate limit to predictability in the same way that deterministic prediction of weather is inherently limited to the order of two weeks or so.
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From page 100... ...
It has been known from inferences about the remote effects of ENSO and from modeling studies that SST in the tropical Pacific affects midlatitude regions.33 To develop skill at midlatitudes, it is important to accurately model these remote effects. What is the relationship between the annual cycle and ENSO predictability?
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From page 101... ...
What are the roles of slowly varying conditions at the Earth's surface (sea ice, SST, snow cover, and soil moisture) in determining the nature of interannual variations in the global atmosphere?
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From page 102... ...
In the continental regions of the higher latitudes (e.g., the United States) , anomalies in soil moisture can persist for periods longer than a season.
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From page 103... ...
Nor are these processes simulated or predicted with sufficient accuracy in numerical models. The manner in which intraseasonal variability affects seasonal to interannual variability, or vice versa, also is unknown.
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From page 104... ...
Currently, seasonal to interannual predictions must assume specified seasonal behavior for these variables, but models that simulate seasonal growth and senescence may be preferable. What representation of runoff is best to calculate evapotranspiration in seasonal to interannual climate prediction models?
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From page 105... ...
It is more important that seasonal to interannual climate models are accurately initiated, as compared to longer-term prediction models. Correct initiation of state variables in hydrological-atmospheric models is thus important, while initiation of soil moisture status in such models is critical.
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From page 106... ...
In what ways can local climate variance be explained in terms of large-scale climate variability? Transformation of large-scale GCM climate predictions to regional and local areas is critical to interdisciplinary scientists and others who wish to know the impacts of climate variability on their areas and activities (e.g., water resources, agriculture, urban development)
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From page 107... ...
These research questions include the following: What are the implications of seasonal to interannual climate forecasts for flood prediction? Opportunities exist in several areas.
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From page 108... ...
Therefore, hydrological drought is determined by the complex interaction of processes that lead to deep soil moisture, and/or groundwater characteristics, throughout the forecast period. What are the implications of seasonal to interannual climate forecasts under "normal" climate conditions?
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From page 109... ...
Methods of using seasonal to interannual climate forecasts under these conditions may well have greater long-term economic benefit than forecasts under less frequent flood or drought situations. LESSONS LEARNED Four central lessons emerge from experience with TOGA and with ENSO prediction.
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From page 110... ...
The TAO array is the first measurement system deployed in the world's oceans that is designed to permanently measure quantities of vital interest to the prediction community and by extension to the oceanographic community. How to maintain the TAO array when no operational agency has responsibility for it is a problem that has occupied the research community in seasonal to interannual prediction for several years.37 The problem is in fact generic: no operational agency supports any measurements other than those taken for weather prediction.
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From page 111... ...
are physical, political, and social; such systems must be studied in both physical and human dimensions. To use seasonal to interannual climate forecasts to our advantage, the identification of applications and the methods of using and communicating the forecasts must be carefully researched.
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From page 112... ...
/GOALS and the Global Energy and Water Cycle Experiment will assure that the research needed to advance seasonal to interannual climate prediction will be done. Observational Requirements The ENSO prediction process -- predicting aspects of SST and corollary variables -- requires data to initialize the coupled models and data to evaluate the skill of the predictions.
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From page 113... ...
The subsurface ocean data are provided by a network of 70 moored TAO arrays in the tropical Pacific Ocean (providing approximately 2 degrees of meridional resolution and 15 degrees of longitudinal resolution)
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From page 114... ...
. Atmospheric general circulation models need to be improved to a stage where, when driven with prescribed observed SST, they simulate realistically the observed annual cycle and interannual variability of the surface wind stress and heat flux, as well as the global atmospheric circulation and rainfall.
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From page 115... ...
Process studies have been conducted to explore physical associations that were difficult to understand but which were critical links in describing the totality of the phenomena. Numerical coupled oceanatmosphere models have been constructed, with moderate success in forecasting seasonal to interannual variability in the tropical Pacific Ocean.
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From page 116... ...
However, they depend in part on details of soil moisture distribution. These details are largely unmeasured and poorly understood at the scales of climate models.
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From page 117... ...
seasonal to interannual prediction program that focuses on the Americas. Downscaling Imperative GCMs are currently the primary tools for studies of climate variability and change.
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From page 118... ...
Although precipitation is the most important determinant of key terrestrial hydrological variables (streamflow, soil moisture, snowpack water content, and evapotranspiration) , the land surface acts as a low-pass nonlinear filter, so that antecedent precipitation as well as current precipitation play important roles in smoothing the effects of climate variability at these timescales.
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From page 119... ...
For hydrological purposes, seasonal to interannual climate forecasts could have at least two important functions. The first is to forecast the evolution of hydrologically important surface variables (especially precipitation and temperature)
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From page 120... ...
. The adequacy of this network for studies of seasonal to interannual variability should be evaluated.
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From page 121... ...
Surface Air and Skin Temperature Observations of surface air temperature are critically important to predict evapotranspiration and snow accumulation and melt. Surface air temperature measurements are routinely collected at NCDC cooperative observer stations as well as at National Weather Service manned observing stations.
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From page 122... ...
In the course of the next decade, a network of surface energy and carbon dioxide flux measurement sites should be established to characterize seasonal to interannual changes in the surface-atmosphere exchanges for major vegetation types in the United States and perhaps globally. Soil Moisture Soil moisture plays a key role in partitioning net radiation into latent, sensible, and ground heat fluxes, particularly in summer.
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From page 123... ...
. The report describes the TAO array and the other remote and in situ measure ment systems providing continuously available data in the tropical Pacific, referred to else where in this report as the ENSO Observing System.
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From page 124... ...
1983. Interannual variability of the equatorial Pacific revisited.
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From page 125... ...
1987. The annual cycle and interannual variability in the tropical Pacific and Indian Ocean region.
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From page 126... ...
Prospects for seasonal-to-interannual climate prediction and applications for sustainable development. Bulletin of the World Meteorological Organization 43(3)
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