1.1 Introduction to CropWatch agroclimatic indicators (CWAIs)

This bulletin describes environmental and crop conditions over the period from January to April 2019, JFMA, referred to as “reporting period”. In this chapter, we focus on 65 spatial “Mapping and Reporting Units” (MRU) which cover the globe, but CWAIs are averages of climatic variables over agricultural areas only inside each MRU. For instance, in the “Sahara to Afghan desert” MRU, only the Nile valley and other cropped areas are considered. MRUs are listed in annex B and serve the purpose of identifying global climatic patterns. Refer to Annex A for definitions and to table A.1 for 2019 JFMA numeric values of CWAIs by MRU).

Although they are expressed in the same units as the corresponding climatological variables,  CWAIs are spatial averages limited to agricultural land and weighted by the agricultural production potential inside each area.  Correlations between variables (RAIN, TMP, RADPAR, BIOMSS) at MRU scale derive directly from climatology. For instance, the positive correlation (R=0.364) between rainfall and temperature results from high rainfall in equatorial, i.e. in warm areas.

We also stress that the reference period, referred to as “average” in this bulletin covers the 15 year period from 2004 to 2018. Although departures from the 2004-2018 are not anomalies (which, strictly, refer to a “normal period” of 30 years), we nevertheless use that terminology. The listed departures from average differ from but are consistent with other sources such as NOAA1 or COPERNICUS2 which use longer and less recent reference period of 30 or 100 years.  The specific reason why CropWatch refers to the most recent 15 years is our focus on agriculture, as already mentioned in the previous paragraph. 15 years is deemed an acceptable compromise between climatological significance and agricultural significance: agriculture responds much faster to persistent climate variability than 30 years, which is a full generation. For “biological” (agronomic) indicators  used in subsequent chapters we adopt an even shorter reference period of 5 years (i.e. 2014-2018) but the BIOMSS indicator is nevertheless compared against the longer 15YA (fifteen years average). This makes provision for the fast response of markets to changes in supply but also to the fact that in spite of the long warming trend, some recent years (e.g. 2008 or 2010-13) were below the trend.

It is stressed that, considering the size of the areas covered in this section, even small departures may have dramatic effects on vegetation and agriculture due to the within zone spatial variability of weather.

1.2 Global overview

Departures from average variables, i.e. anomaly patterns characterize the current reporting period more meaningfully than the averages themselves. RAIN was below average in about 60% of the MRUs, resulting in RAIN being 2% above the average value of the 15-year reference period (2004-2018). TEMP was average (just 0.1°C above average) while RADPAR was slightly above average.  The current calculation procedure of the biomass production potential BIOMSS depends on rainfall and temperature. During the current reporting period 80% of its variations can be ascribed to RAIN variations and a couple of % only to TEMP.  As a result, the global average is 1% above normal (55% of values are above normal).

Compared with previous JFMA periods, especially in 2017 and, to a lesser extent, the 2018, rainfall depths were much closer to the corresponding 15 years average: +13% in 2017, +8% in 2018 and just +2% in 2019 (Figure 1.1).  For RADPAR, the current value of +1% follows two negative departures in 2017 (-2%) and 2018 (-5%). Similarly, the global TEMP is slightly positive (departure +0.1°C after negative departures in 2017 (-0.2°C) and in 2018 (-0.1°C).   When looking at weighted averages (Table 1.1), world average values are even closer to average.

Although, the current JFMA reporting period was closer to “average” than during the previous seasons, significant continental differences are observed, as illustrated in Table 1.1. RAIN deficits were large in large Oceania (-23%, during summer, mostly in the east and south) and moderate in central America (late and end of growing season), south America (where the reporting period corresponds to late summer crop season in the southern temperature areas) and in Africa where JFMA covers the end of the Mediterranean winter season and the main maize growing season in southern Africa. Well above average precipitation fell over north America (+12%), central (+11%) and eastern Asia (+10%)

Figure 1.1: global departure from recent 15 year average of the RAIN, TEMP and RADPAR indicators since 2017 JFMA period (average of 65 MRUs, unweighted)

Table 1.1: Departures from the recent 15-year average of CropWatch agroclimatic indicators over regional MRU groups during JFMA. Within each group, averages are weighted by the agricultural area of individual MRUs. “Others” include five non agricultural areas shown in white in the map.

Largely uncorrelated temperatures were recorded over north America (-0.9°C) with low sunshine (-4%) while remaining areas of the continent had a smaller temperature deficit (-0.3°C). The largest sunshine deficits next to N. America occurred in central and eastern Asia (-4% and -3%, respectively).

Although the areas listed as “others” are mostly irrelevant for cropping, it is nevertheless interesting to observe large positive rainfall and temperature departure (+7% and +2.2°C, respectively) both resulting from very anomalous conditions in Boreal north America where RAIN was up 21% and TEMP exceeded average by 3.5°C, which is very significant and locally led to unseasonable snow-melt.

Biomass departures roughly follow rainfall anomalies except in north America, resulting from the combined effect of low temperature and low sunshine. The increase is spectacular (+18%) at the highest latitudes.

1.3 Rainfall and BIOMSS anomalies (figures 1.2 and 1.3)

Figure 1.2. Global map of rainfall anomaly (as indicated by the RAIN indicator) by CropWatch Mapping and Reporting Unit (MRU), departure from 15YA between between January and April 2019

Figure 1.3. Global map of biomass production potential anomaly (as indicated by the BIOMSS indicator) by CropWatch Mapping and Reporting Unit (MRU), departure from 15YA between between January and April 2019

Marked rainfall deficits in excess of 30% occurred in Oceania (New Zealand MRU 56, -32%; Nullarbor to Darling in south-west Australia MRU 55, -40%), In Queensland to Victoria (MRU 54), which includes major agricultural areas, the deficit was lower at 23 %, 171 mm instead of the average 222 mm). All these areas have not started their main growing season and the impact on production is currently neutral, even if soil moisture is lower than expected.  The same applies to a large extent in Central America (MRU 17  Sierra Madre, -37%) and northern South America (MRU 19, 33%). In the Semiarid Southern cone (MRU 28, -30%) crops play a minor part but the shortage or rainfall has affected rangelands. In the tropical southern Chinese island of Hainan (MRU 33, -39%) the main growing season is just starting but initial conditions are water water stressed. The most severe impact of drought is likely to have occurred in MRU 07, the north African Mediterranean. Especially in the Maghreb, the end of the main wheat and barley season coincides with the reporting period and the water deficit (-33%) is bound to have affected the maturity of crops.

Less severe, but nevertheless significant deficits affected southern Asia (MRU 45, -13% in southern Asia; MRU 50, -12% continental south-East Asia) and eastern Africa (MRU 02,  the east-African Highlands with RAIN down 10%; MRU 04, -17%, the Horn of Africa).

Large positive rainfall anomalies occurred in two disjoined areas in the North America and in an area extending from west Africa to central and eastern Asia. The area was highlighted in most recent CropWatch bulletins  as it seems to have become a permanent feature. In northern America, abundant precipitation affected MRUs 13 and 16, the Corn Belt and the west coast, with excesses of 34% and 32%, respectively, two important agricultural areas which have suffered from water logging and floods.  In Asia, the highest precipitation was recorded from the eastern edge of the Mediterranean the second area (MRU 31, Western Asia, rainfall up 33%) to China: Huanghuaihai (MRU 34, +34%), southern China (MRU 40, RAIN +43%) and Taiwan (MRU 42, RAIN +45%). In between, we need to mention the Loess region (MRU 36), Gansu-Xinjiang (MRU 32) and Southern Mongolia (MRU 47) with excesses reaching +35%, +61% and +170%, respectively. While the Loess region is a major agricultural area, pastoralism prevails in semi-arid MRUs 32 and 46. In all areas, the precipitation has replenished soil  moisture and created favourable conditions for winter spring growth, rangeland development and river flows.

In general, the departures from average of biomass development potential follow precipitation departures, within limits due to the impact of temperature. Among the low rainfall areas (deficit at least 20%), different behaviours of RAIN and BIOMSS only occur in Eastern Central Asia (MRU 52), which covers essentially the northern half of Mongolia, the Republic of Buryatia and the Amur Oblast, where winter crops are marginal productions. MRU 52 had a precipitation deficit of 27%, but BIOMSS was down only 5% due to the large positive temperature anomaly (+2.4°C). Temperatures, however, remained well below freezing. In the Corn Belt, Taiwan and Gansu-Xinjiang, which are all large rainfall excess areas, the biomass potential increased much less than precipitation, (BIOMSS variation of -4%, +23 and +38%, respectively) because precipitations have reached high values above which BIOMSS increases no longer respond to RAIN increases.

1.4 Temperatures (Figure 1.4)

Figure 1.4. Global map of temperature anomaly (as indicated by the TEMP indicator) by CropWatch Mapping and Reporting Unit (MRU), departure from 15YA between between January and April 2019

The largest area of spatially consistent positive temperature anomalies occurred in Eurasia, from non-Mediterranean western Europe (MRU 60, +0.5°C) to southern Japan and Korea (MRU 46, +0.6°C). It embeds MRUS with larger anomalies in the west (MRU 58, Ukraine to Ural mountains) and in the east (MRUs 52, eastern Central Asia; MRU 38, North-East China and MRU 35, Inner Mongolia) where the positive temperature anomalies reached 1.7°C, 2.4°C, 3.0°C and 1.6°C, respectively.

The northern half of Africa, much of north America and of South America had cool weather with departures from average in the range from -0.5°C to -1,5°C. The coldest area that deserves to be mentioned is MRU 12, the northern Great Plains, -2.3°C below average, as well the adjacent MRUs of British Columbia to Colorado (MRU 11, -1.5°C below average) and, to a lesser extent, the Corn Belt (MRU 13, -0.7°C).

1.5 RADPAR (sunshine, Figures 1.5)

Figure 1.5. Global map of photosynthetically active vradiation anomaly (as indicated by the RADPAR indicator) by CropWatch Mapping and Reporting Unit (MRU), departure from 15YA between between January and April 2019

The situation of sunshine is easily summarised: low RADPAR occurred (1) from west Africa to eastern Asia, (2) northern America and (3) the main temperature summer crop areas in south America. Virtually all other areas somehow experienced above-average radiation.

In the first (1), lowest values occur in eastern Asia (MRU 37, Lower Yangtze -15%; MRU 34, Huanghuaihai, -4% and MRU 41, South-West China with -3%) and in western-central Asia, especially mountain areas. They include, in addition to MRU 31 (Western Asia, -6%), the Pamir area (MRU 30, -7%), the Caucasus (MRU 29, -4%) and the Ural to Altai mountain ranges (MRU 62,  -3%).

The second (2) includes five MRUs with values from -6% in the two first to 4% in the last: MRU 16,    West Coast; MRU 14, Cotton Belt to Mexican Nordeste; MRU 18, south-western US and Northern Mexican highlands; MRU 13, the Corn Belt and MRU 12, the Northern Great Plains.

The third (3) includes MRU 25, Central-north Argentina with RADPAR down 6%, as well as the major summer crop growing area of the Pampas (MRU 26) at 4%. This includes south-eastern Brazil, Uruguay and the north-eastern provinces of Argentina.

The most abnormally sunny regions include New Zealand (MRU 56) and Hainan Island (MRU 33) where the excess sunshine reached 9 and 17%, respectively.

1.6 Combinations of anomalies

The above-mentioned high sunshine areas in MRUs 33 and 56 were also, logically,  characterised by dry conditions and, at least for Hainan (MRU 33) by significantly warmer than average temperature (+2.0°C).

About half the areas where weather was globally atypical for the JFMA period occurred in Asia, and more specifically in China. This includes low rainfall with high temperature and abundant sunshine in Hainan (MRU 33), North-East China (MRU 38) and eastern-central Asia (MRU 38). Another group of MRUs had high rainfall with either very low RADPAR (Lower Yangtze, MRU 37) or unseasonably warm weather in Inner Mongolia (MRU 35), Taiwan (MRU 42) and Gansu-Xinjiang (MRU 32). On the American continent, two mostly pastoral areas were dry and cold in the south (MRU 28, the Semi-arid Southern Cone and MRU 27, Western Patagonia) or wet and cold with low sunshine in one of the major global agricultural areas, the Corn Belt (MRU 13).

In Africa, both the Sahel (MRU 08) and the Sahara to Afghan Desert (MRU 64) has relatively cool weather (by local standards!)  but the second was wetter than average. Southern Australia was dry but cooler than expected in the west and warm in the east.