{"id":614,"date":"2014-12-15T21:12:04","date_gmt":"2014-12-15T21:12:04","guid":{"rendered":"http:\/\/www.jamesrising.net\/blog\/?p=614"},"modified":"2014-12-15T21:12:04","modified_gmt":"2014-12-15T21:12:04","slug":"negative-result-country-wide-growing-degree-days","status":"publish","type":"post","link":"http:\/\/www.jamesrising.net\/blog\/?p=614","title":{"rendered":"Negative result: country-wide growing degree-days"},"content":{"rendered":"

I put this here as a warning. While growing degree-days (GDD) are well-known as an effective model to predict yields, they don’t perform so hot at the country-scale.<\/p>\n

I used mean temperature GDDs, between 8 and 24 degrees C, estimated at many locations from station data, and then using the weighted average by production within each country. Here are the results:<\/p>\n\n\n\n\n\n\n\n\n\n\n\n
Statistical models<\/caption>\n
<\/th>\nBarley<\/b><\/th>\nMaize<\/b><\/th>\nMillet<\/b><\/th>\nRice<\/b><\/th>\nSorghum<\/b><\/th>\nWheat<\/b><\/th>\n<\/tr>\n
GDD \/ 1000<\/td>\n-0.03<\/td>\n0.01<\/td>\n-0.07**<\/sup><\/td>\n0.08<\/td>\n0.04*<\/sup><\/td>\n-0.08***<\/sup><\/td>\n<\/tr>\n
<\/td>\n(0.01)<\/td>\n(0.01)<\/td>\n(0.03)<\/td>\n(0.06)<\/td>\n(0.02)<\/td>\n(0.02)<\/td>\n<\/tr>\n
Precip. (m)<\/td>\n0.09<\/td>\n0.11***<\/sup><\/td>\n0.12*<\/sup><\/td>\n0.02<\/td>\n0.14***<\/sup><\/td>\n-0.04<\/td>\n<\/tr>\n
<\/td>\n(0.05)<\/td>\n(0.03)<\/td>\n(0.05)<\/td>\n(0.03)<\/td>\n(0.04)<\/td>\n(0.04)<\/td>\n<\/tr>\n
Country Cubic<\/td>\nY<\/td>\nY<\/td>\nY<\/td>\nY<\/td>\nY<\/td>\nY<\/td>\n<\/tr>\n
R2<\/sup><\/td>\n0.95<\/td>\n0.97<\/td>\n0.91<\/td>\n0.97<\/td>\n0.92<\/td>\n0.96<\/td>\n<\/tr>\n
Adj. R2<\/sup><\/td>\n0.94<\/td>\n0.96<\/td>\n0.90<\/td>\n0.97<\/td>\n0.91<\/td>\n0.95<\/td>\n<\/tr>\n
Num. obs.<\/td>\n1639<\/td>\n3595<\/td>\n1516<\/td>\n1721<\/td>\n2300<\/td>\n1791<\/td>\n<\/tr>\n
***<\/sup>p < 0.001, **<\/sup>p < 0.01, *<\/sup>p < 0.05<\/span><\/td>\n<\/tr>\n<\/table>\n

As you can see, for most crops, these GDDs aren’t even significant, and as frequently negative as positive. This defies a century of agricultural research, but the same data at a fine spatial scale seems to work just fine.<\/p>\n","protected":false},"excerpt":{"rendered":"

I put this here as a warning. While growing degree-days (GDD) are well-known as an effective model to predict yields, they don’t perform so hot at the country-scale. I used mean temperature GDDs, between 8 and 24 degrees C, estimated at many locations from station data, and then using the weighted average by production within … Continue reading Negative result: country-wide growing degree-days<\/span> →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[10,14,15],"class_list":["post-614","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-ifttt","tag-james-rising","tag-pro"],"_links":{"self":[{"href":"http:\/\/www.jamesrising.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/614","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.jamesrising.net\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.jamesrising.net\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.jamesrising.net\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.jamesrising.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=614"}],"version-history":[{"count":1,"href":"http:\/\/www.jamesrising.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/614\/revisions"}],"predecessor-version":[{"id":615,"href":"http:\/\/www.jamesrising.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/614\/revisions\/615"}],"wp:attachment":[{"href":"http:\/\/www.jamesrising.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=614"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.jamesrising.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=614"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.jamesrising.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=614"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}