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274 assessment of climate change in the southwest united statesFigure 13.6 Anthropogenic heat flux estimates for three Southwest cities, shown in wattsper square meter. Urban built-up (no vegetation), urban mesic residential (well-watered flood oroverhead irrigated), and urban xeric residential (drought-adapted vegetation with drip irrigation) aredistinguished by their type of vegetation and irrigation, listed in parentheses. Adapted from Sailor andLu (2004) and Grossman-Clarke et al. (2005).rural areas. However, the annual frequency of hot nights would increase more in the citythan in the rural areas for the CO 2doubling scenario. In the city of Los Angeles the numberof hot nights would increase by two days with 20 W/m 2 of anthropogenic heatingand by ten days with 60 W/m 2 .About 60 million people live in the Southwest, the majority of whom reside in majormetropolitan urban centers and consume the majority of goods and services. As indicatedbefore, good information is lacking about the direct and indirect GHG emissionsfrom urban populations. However, new studies have shown that the net emissions associatedwith imports and exports of goods and services in the United States are substantial(Peters and Hertwich 2008; Davis and Caldeira 2010), as shown in Figure 13.7.Estimates of consumption-based emissions (which take into account net imports andexports of goods and services) for the United States are about 12% higher than production-basedinventories (i.e., conventional inventories) (Davis and Caldeira 2010). Preparingconsumption-based inventories for cities should be a priority to identify potentialunrecognized sources of indirect emissions. By implementing life-cycle analysis forgoods and services, such information could be developed.