Temperature changes related to greenhouse gas warming of the Earth’s climate are alarming to farmers, as well as consumers of agricultural products. Climate scientists have teamed with botanists and agricultural scientists to determine the potential impact of warmer temperatures on many different crop varieties. While almost all crops will be affected to an extent, some notably desirable crops, such as coffee, wine grapes, cacao (for chocolate), maple trees (for syrup), and apples, are considered to be highly vulnerable. Climate scientists don’t expect these crops will disappear entirely, but they do expect them to become more difficult to produce and, thus, more expensive.
Another crop that can be put on this list is tea, which is the world’s second favorite beverage after water. The finest quality teas grown in India are found on the slopes of the Himalayan Mountains. Mountain slopes around the world are also hot spots for climate change, because changes of only a few tenths of a degree can significantly alter the altitude and conditions where plants can thrive. Warmer temperatures can make crops more vulnerable to insect pests, change rainfall patterns and amounts, affect the amount of water stored in the soil, and change the length of growing seasons.
Recent studies have indicated that climate change is evident in the tea-growing regions of India. The availability of many different climate variables provided by the Global Land Data Assimilation System (GLDAS) back to the year 1948 (from the GLDAS Version 2 “NOAH” model) makes it possible to examine climate trends over decades. The area selected for analysis with the Giovanni-3 system (http://giovanni.gsfc.nasa.gov/) is shown on the map. This particular area includes Darjeeling, India, which lends its name to Darjeeling tea, grown at altitudes between 800-2000 meters. Higher altitudes are considered to be favorable for yielding higher quality teas. The GLDAS average surface temperature data were used to generate a time series from 1948 to 2010.
Figure 1 shows that, when all the months from January 1948 to 2010 are plotted, a temperature trend is not readily apparent.
Figure 1: Time series of GLDAS Version 2 NOAH model average surface temperature data, 1948-2010 (top), for the Himalayan foothills region (bottom). The approximate location of Darjeeling, India is shown by the green star. (Click on the images to view them full-size.)
Close examination of these data, however, indicated there might be a detectable change in the highest and lowest temperatures. So, in an Excel spreadsheet, the data were regrouped by month (i.e., all the values for a particular month for all the years) and then plotted for individual months. Figure 2 shows these regrouped data for August. Because the warmest temperatures of summer occur in August, the warming trend that is evident in this time series could indicate increasing stress on the tea plants. Increasing temperatures in the wider region might also affect the amount of meltwater from Himalayan glaciers, change the relative humidity and cloud cover, and increase soil erosion by heavier rainfall events. All of these factors indicate that climate change could be brewing trouble for India’s tea crop.
Figure 2. Time series of GLDAS average surface temperature (K) for August, 1948-2010, in the Himalayan foothills region.
Giovanni-4 (http://giovanni.gsfc.nasa.gov/giovanni/) is still in development. Many data sets and data products are in the process of being added to the system. One of the data analysis capabilities provided by Giovanni-4 is the generation of monthly (e.g., Fig. 2) and seasonal time series. When all of the GLDAS data are available in Giovanni-4, the system will allow the creation of monthly time series directly, so that it will be possible to examine data plots of this type without the need for additional software.
This time series analysis was initially created for a supplementary Data-enhanced Investigations for Climate Change (DICCE) guide document, entitled “How to identify potential climate trends in short-term satellite (and related) data sets available in DICCE-Giovanni” (PDF). The document provides examples for teachers and students that demonstrate how to look for examples of climate change with the different data products provided in the DICCE-Giovanni portal.
Picture of Darjeeling tea by Aron Gustafson on Flickr, Creative Commons License 2.0.