We present an improved design of a wavelength-tunable single-mode laser array based on a high order surface grating with non-uniformly spaced slots. The laser array consists of 12 slotted single-mode lasers. The fabricated device exhibits a quasi-continuous tuning range of more than 36 nm over the temperature range from 10°C - 45°C covering the full C-band. All lasers in the array have stable single-mode operation with side mode suppression ratio of 50 dB due to the modified slot design. A spectral linewidth of less than 500 kHz was obtained for all channels in the array.
An agricultural water conservation policy prevalent worldwide encourages producers to improve on-farm irrigation efficiency. Contrary to intention, increasing empirical evidence reveals that this policy may set an 'irrigation efficiency trap' that worsens water crises by reducing water supplies and jeopardizing economic growth. We derive a pair of testable hydrologic-economic conditions required for the sustained existence of the trap. We do so by modeling an agroindustrial economy patterned after a region (Snake River Plain aquifer, Idaho, USA) that has fallen into the trap. An agricultural sector withdraws water to irrigate crops, and the difference between water withdrawals and the amount consumed by crops (return flow) recharges water supplies used in industrial production. The conditions require that: (1) The rate of return of water in industrial production outweighs the rate of return of water withdrawn to food production; and (2) An inequality relating the elasticities of food production with respect to irrigation withdrawals and irrigation efficiency hold in a particular direction. If empirical testing of these conditions provides evidence of the sustained existence of the irrigation efficiency trap in a given region, policy-makers are well-advised to target more potentially effective agricultural water conservation measures such as reducing irrigated acreage, switching to crops requiring less water, or irrigating current crops at a deficit.
Ecosystem services are benefits people derive from resources in ecosystems. Playa lakes in the Southern High Plains region of North America provide several ecosystem services for humans, including recharge to the Ogallala aquifer. The Ogallala aquifer occupies 450,000 km 2 , it is part of eight states, and provides irrigation water to over 25% of the irrigated land in the United States. The recharge provided by playas potentially makes them important and valuable in this region. We develop an econometric model (with spatial aspects) to determine how playas affect the water level of irrigation wells and estimate the economic value to farmers of playa ecosystem services in recharging the water in those wells. We find that, in some instances, additional playa surface area may have a small but statistically significant effect on well drawdown (and, we infer, on recharge) on nearby wells, but that the value of the additional water is likely too small to significantly affect private management decisions. Because of lack of appropriate data, these results are of only limited applicability. We therefore identify a need for more research on the effects of management of sedimentation of playa wetlands as a key component that may improve the findings reported here.
Climate change and windborne dust are expected to change snowmelt timing. Dust from agricultural activities is estimated to cause snow to melt two to four weeks earlier in some regions. Early snowmelt may decrease deliveries of irrigation water when reservoirs provide flood protection and irrigation water. To date, the quantity decrease has not been determined. We identify when early snowmelt causes earlier water release, and calculate the quantity decrease in water deliveries downstream. Irrigation reductions are negligible unless the dam capacity is less than twice the quantity of annual runoff, and unless snowmelt occurs more than four weeks early.
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