observed EC. Consequently, the results can be interpreted as conservative predictions of the risk of high salinity.

Using the coefficients shown in figure 5 (based on 30 percent cropland), annual changes in NPP, and the EC data set described above, we estimate annual losses in agricultural productivity due to EC for each 0.5x0.5‐degree gridcell where cropland exceeds 30 percent of landcover, globally. We then convert the resulting loss of NPP to kilocalorie equivalents, following Strobl and Strobl (2011) and Imhoff et al. (2014). Globally, average annual losses from 2001‐2013 due to saline water total 124 trillion kilocalorie‐ equivalents. In total, assuming 2,000 calories/person/day, these calories represent enough food to cover the food budgets of 170 million people, annually.

The distribution of these losses is shown in Figure 7. With the exception of Sub‐Saharan Africa, where most food production is rainfed, all continents have large hotspots. Very wet regions, such as the Amazon basin, Southeast Asia, and the southeastern United States also avoid losses from salinity, despite being important agricultural zones. Figure 8 aggregates losses by countries and shows further that the impact is generally not correlated with development level. The United States is the country with the largest loss of agricultural production, losing the equivalent of 32 trillion calories per year, more than double that of Argentina, the country with the next largest losses.

# 7. Conclusions

Addressing water quality needs for agriculture is a tremendous challenge. With agriculture responsible for 70 percent of freshwater abstractions globally, and the need for an additional 20 percent increase in water withdrawals by 2050 to feed a population of 9 billion, the problems of water scarcity often overshadow those of water quality. Nevertheless, the results in this paper demonstrate that yield losses due to saline water are significant and deserve more attention.

There is no one‐size‐fits‐all solution to reducing salinity in irrigation waters. Solutions vary greatly by location and context. In some regions, it will require better irrigation management, to ensure that the salt balance remains low and steady. Well‐designed irrigation drainage systems can accomplish this while also preventing waterlogging, which can also be harmful to crop productivity. Still, drainage systems must be carefully designed to ensure that they do not remove _too much_ salt from soil layers. If draining systems do not specifically target the root layer of the soil, they may end up removing more salt from the soil than was applied by irrigation. This will cause an increase in the salt load of the water leaving the field, and impact downstream water users (Christen, <mark>Ayars, and Hornbuckle</mark> 2001).

Dealing with over‐extraction is also important for reducing the occurrence of salinity in water. Over‐ extraction can exacerbate water salinity through reduced dilution of downstream water. Salt, at low levels of concentration, can be benign—it is only once those concentration levels become too high that productivity declines. Removing less water from the system is therefore the easiest way to prevent concentrations from becoming too high. The link between over‐extraction and salinity also has the potential to lead to a vicious cycle of salinization if higher salinity levels lead to increased extraction, and therefore increased salinity. The urgency is particularly acute for countries already exposed to malnutrition and climate variability, as in the case of South Asia.

Adaptation through crop choice decisions becomes necessary when reducing salinity in water is too difficult or costly. As discussed above, crops have different tolerance levels to saline water, with some 9