{"id":158,"date":"2014-12-15T21:03:24","date_gmt":"2014-12-15T21:03:24","guid":{"rendered":"https:\/\/existencia.org\/pro\/?p=158"},"modified":"2014-12-15T21:03:24","modified_gmt":"2014-12-15T21:03:24","slug":"negative-result-country-wide-growing-degree-days","status":"publish","type":"post","link":"https:\/\/existencia.org\/pro\/?p=158","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 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[3],"tags":[],"class_list":["post-158","post","type-post","status-publish","format-standard","hentry","category-research"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p4Zh9E-2y","_links":{"self":[{"href":"https:\/\/existencia.org\/pro\/index.php?rest_route=\/wp\/v2\/posts\/158","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/existencia.org\/pro\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/existencia.org\/pro\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/existencia.org\/pro\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/existencia.org\/pro\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=158"}],"version-history":[{"count":0,"href":"https:\/\/existencia.org\/pro\/index.php?rest_route=\/wp\/v2\/posts\/158\/revisions"}],"wp:attachment":[{"href":"https:\/\/existencia.org\/pro\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=158"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/existencia.org\/pro\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=158"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/existencia.org\/pro\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=158"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}