A New Indicator for Global Food Security Assessment: Harvested Area Rather Than Cropland Area

Cropland area has long been used as a key indicator of food security.However,grain yield is not solely controlled by the area of the cropland.Therefore,we proposed a new indicator to assess food security.Results show that from 1992 to 2004,the global cropland area increased by 840200 km^(2)(99.4%),but the grain yield increased only by 310 million t(29.1%);and from 2004 to 2015,the cropland area decreased by 39000 km^(2)(4.64%),but the grain yield increased by 370 million t(70.84%).This result showed that grain yield was not linearly correlated with cropland area,and delimiting the threshold of cropland protection may not guarantee food security.Combined with further correlation analysis,we found that the increase in the global grain yield was more closely related to the harvested area(R^(2)=0.94),which indicated that the harvested area is a more scientific and accurate indicator than cropland area in terms of guaranteeing food security.Therefore,if governments want to ensure the food security,they should choose a new and more accurate indicator:harvested area rather than cropland area.

Life cycle assessment of low impact development technologies combined with conventional centralized water systems for the City of Atlanta, Georgia

Low-impact development （LID） technologies, such as bioretention areas, rooftop rainwater harvesting, a_nd xeris_caping can co_ntrol stormwater runoff, supply non-potable water, and landscape open space.TillS study examines a hybrid system （HS） that combines LID technologies with a centralized water system to lessen the burden on a conventional system （CS）. CS is defined as the stormwater collection and water supply infrastructure, and the conventional landscaping choices in the City of Atlanta. The study scope is limited to five single-family residential zones （SFZs）, classified R-1 through R-5, and four multi-family residential zones （MFZs）, classified RG-2 through RG-5. Population density increases from 0.4 （R-1） to 62.2 （RG-5） persons per 1,000 m2. We performed a life cycle assessment （LCA） comparison of CS and HS using TRACI 2.1 to simulate impacts on the ecosystem, human health, and natural resources. We quantified the impact of freshwater consumption using the freshwater ecosystem impact （FEI） indicator. Test results indicate that HS has a higher LCA single score than CS in zones with a low population density; however, the difference becomes negligible as population density increases. Incorporating LID in SFZs and MFZs can reduce potable water use by an average of 50%. and 25%,respectively.; however, water savings are negligible in zones with high population density （i.e., RG-5） due to the diminished surface area per capitaavailable for LID technoogies. The results demonstrate that LID technologies effectively reduce outdoor water demand and therefore would be a good choice to decrease the water consumption impact in the City of Atlanta.